### 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
super(GalaxyCLI, self).run()
        self.galaxy = Galaxy()
        def server_config_def(section, key, required, option_type):
            config_def = {
                'description': 'The %s of the %s Galaxy server' % (key, section),
                'ini': [
                    {
                        'section': 'galaxy_server.%s' % section,
                        'key': key,
                    }
                ],
                'env': [
                    {'name': 'ANSIBLE_GALAXY_SERVER_%s_%s' % (section.upper(), key.upper())},
                ],
                'required': required,
                'type': option_type,
            }
            if key in SERVER_ADDITIONAL:
                config_def.update(SERVER_ADDITIONAL[key])
            return config_def
        galaxy_options = {}
        for optional_key in ['clear_response_cache', 'no_cache']:
            if optional_key in context.CLIARGS:
                galaxy_options[optional_key] = context.CLIARGS[optional_key]
        config_servers = []
        
        server_list = [s for s in C.GALAXY_SERVER_LIST or [] if s]
        for server_priority, server_key in enumerate(server_list, start=1):