### 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
@classmethod
    def setUpClass(cls):
        role_skeleton_path = os.path.join(os.path.split(__file__)[0], 'test_data', 'role_skeleton')
        cls.setUpRole('delete_me_skeleton', skeleton_path=role_skeleton_path, use_explicit_type=True)
    @classmethod
    def tearDownClass(cls):
        cls.tearDownRole()
    def test_empty_files_dir(self):
        files_dir = os.path.join(self.role_dir, 'files')
        self.rtTrue(os.path.isdir(files_dir))
        self.rtListEqual(os.listdir(files_dir), [], msg='we expect the files directory to be empty, is ignore working?')
    def test_template_ignore_jinja(self):
        test_conf_j2 = os.path.join(self.role_dir, 'templates', 'test.conf.j2')
        self.rtTrue(os.path.exists(test_conf_j2), msg="The test.conf.j2 template doesn't seem to exist, is it being rendered as test.conf?")
        with open(test_conf_j2, 'r') as f:
            contents = f.read()
        expected_contents = '[defaults]\ntest_key = {{ test_variable }}'
        self.rtEqual(expected_contents, contents.strip(), msg="test.conf.j2 doesn't contain what it should, is it being rendered?")
    def test_template_ignore_jinja_subfolder(self):
        test_conf_j2 = os.path.join(self.role_dir, 'templates', 'subfolder', 'test.conf.j2')
        self.rtTrue(os.path.exists(test_conf_j2), msg="The test.conf.j2 template doesn't seem to exist, is it being rendered as test.conf?")
        with open(test_conf_j2, 'r') as f:
            contents = f.read()
        expected_contents = '[defaults]\ntest_key = {{ test_variable }}'
        self.rtEqual(expected_contents, contents.strip(), msg="test.conf.j2 doesn't contain what it should, is it being rendered?")
    def test_template_ignore_similar_folder(self):
        self.rtTrue(os.path.exists(os.path.join(self.role_dir, 'templates_extra', 'templates.txt')))
    def test_skeleton_option(self):