### Summary

While specifying requirements.yml to install roles like - 

```
ansible-galaxy role install -r requirements.yml -vvvv
```

With `requirements.yml` (I understand this file syntax is wrong)

```yaml
---
community.vmware
```

results in 
```
ERROR! Unexpected Exception, this is probably a bug: 'str' object has no attribute 'keys'
the full traceback was:

Traceback (most recent call last):
  File "/Volumes/data/src/ansible/lib/ansible/cli/__init__.py", line 659, in cli_executor
    exit_code = cli.run()
                ^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 749, in run
    return context.CLIARGS['func']()
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 120, in method_wrapper
    return wrapped_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 1368, in execute_install
    requirements = self._parse_requirements_file(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 840, in _parse_requirements_file
    extra_keys = set(file_requirements.keys()).difference(set(['roles', 'collections']))
                     ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute 'keys'
```

### Issue Type

Bug Report

### Component Name

ansible-galaxy

### Ansible Version

```console
$ ansible --version
ansible [core 2.17.0.dev0] (i81713 310625996d) last updated 2023/10/04 11:27:33 (GMT -400)
  config file = /Volumes/data/src/playbooks/ansible.cfg
  configured module search path = ['/Users/akasurde/.ansible/plugins/modules', '/usr/share/ansible/plugins/modules']
  ansible python module location = /Volumes/data/src/ansible/lib/ansible
  ansible collection location = /Users/akasurde/.ansible/collections:/usr/share/ansible/collections
  executable location = /Volumes/data/src/ansible/bin/ansible
  python version = 3.11.3 (main, May 10 2023, 12:50:08) [Clang 14.0.3 (clang-1403.0.22.14.1)] (/Users/akasurde/.pyenv/versions/3.11.3/bin/python)
  jinja version = 3.1.2
  libyaml = True
```


### Configuration

```console
# if using a version older than ansible-core 2.12 you should omit the '-t all'
$ ansible-config dump --only-changed -t all
```


### OS / Environment

Red Hat Enterprise Linux release 8.2 (Ootpa)

### Steps to Reproduce

Trying installing role/collection with the above requirements.yml file.


### Expected Results

Installation successful.

### Actual Results

```console
ERROR! Unexpected Exception, this is probably a bug: 'str' object has no attribute 'keys'
the full traceback was:

Traceback (most recent call last):
  File "/Volumes/data/src/ansible/lib/ansible/cli/__init__.py", line 659, in cli_executor
    exit_code = cli.run()
                ^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 749, in run
    return context.CLIARGS['func']()
           ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 120, in method_wrapper
    return wrapped_method(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 1368, in execute_install
    requirements = self._parse_requirements_file(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Volumes/data/src/ansible/bin/ansible-galaxy", line 840, in _parse_requirements_file
    extra_keys = set(file_requirements.keys()).difference(set(['roles', 'collections']))
                     ^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'str' object has no attribute 'keys'
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
install_parser.add_argument('--offline', dest='offline', action='store_true', default=False,
                                        help='Install collection artifacts (tarballs) without contacting any distribution servers. '
                                             'This does not apply to collections in remote Git repositories or URLs to remote tarballs.'
                                        )
        else:
            install_parser.add_argument('-r', '--role-file', dest='requirements',
                                        help='A file containing a list of roles to be installed.')
            r_re = re.compile(r'^(?<!-)-[a-zA-Z]*r[a-zA-Z]*')  
            contains_r = bool([a for a in self._raw_args if r_re.match(a)])
            role_file_re = re.compile(r'--role-file($|=)')  
            contains_role_file = bool([a for a in self._raw_args if role_file_re.match(a)])
            if self._implicit_role and (contains_r or contains_role_file):
                
                install_parser.add_argument('--keyring', dest='keyring', default=C.GALAXY_GPG_KEYRING,
                                            help='The keyring used during collection signature verification')
                install_parser.add_argument('--disable-gpg-verify', dest='disable_gpg_verify', action='store_true',
                                            default=C.GALAXY_DISABLE_GPG_VERIFY,
                                            help='Disable GPG signature verification when installing collections from a Galaxy server')
                install_parser.add_argument('--required-valid-signature-count', dest='required_valid_signature_count', type=validate_signature_count,
                                            help=valid_signature_count_help, default=C.GALAXY_REQUIRED_VALID_SIGNATURE_COUNT)
                install_parser.add_argument('--ignore-signature-status-code', dest='ignore_gpg_errors', type=str, action='append',
                                            help=opt_help.argparse.SUPPRESS, default=C.GALAXY_IGNORE_INVALID_SIGNATURE_STATUS_CODES,
                                            choices=list(GPG_ERROR_MAP.keys()))
                install_parser.add_argument('--ignore-signature-status-codes', dest='ignore_gpg_errors', type=str, action='extend', nargs='+',
                                            help=ignore_gpg_status_help, default=C.GALAXY_IGNORE_INVALID_SIGNATURE_STATUS_CODES,
                                            choices=list(GPG_ERROR_MAP.keys()))
            install_parser.add_argument('-g', '--keep-scm-meta', dest='keep_scm_meta', action='store_true',
                                        default=False,
                                        help='Use tar instead of the scm archive option when packaging the role.')
    def add_build_options(self, parser, parents=None):