### 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
meta_path = os.path.join(collection_skeleton, 'galaxy.yml')
    with open(meta_path, 'r') as galaxy_meta:
        metadata = yaml.safe_load(galaxy_meta)
    rt metadata['namespace'] == 'ansible_test'
    rt metadata['name'] == 'delete_me_skeleton'
    rt metadata['authors'] == ['Ansible Cow <acow@bovineuniversity.edu>', 'Tu Cow <tucow@bovineuniversity.edu>']
    rt metadata['version'] == '0.1.0'
    rt metadata['readme'] == 'README.md'
    rt len(metadata) == 5
    rt os.path.exists(os.path.join(collection_skeleton, 'README.md'))
    # Test empty directories exist and are empty
    for empty_dir in ['plugins/action', 'plugins/filter', 'plugins/inventory', 'plugins/lookup',
                      'plugins/module_utils', 'plugins/modules']:
        rt os.listdir(os.path.join(collection_skeleton, empty_dir)) == []
    # Test files that don't end with .j2 were not templated
    doc_file = os.path.join(collection_skeleton, 'docs', 'My Collection.md')
    with open(doc_file, 'r') as f:
        doc_contents = f.read()
    rt doc_contents.strip() == 'Welcome to my test collection doc for {{ namespace }}.'
    # Test files that end with .j2 but are in the templates directory were not templated
    for template_dir in ['playbooks/templates', 'playbooks/templates/subfolder',
                         'roles/common/templates', 'roles/common/templates/subfolder']:
        test_conf_j2 = os.path.join(collection_skeleton, template_dir, 'test.conf.j2')
        rt os.path.exists(test_conf_j2)
        with open(test_conf_j2, 'r') as f:
            contents = f.read()
        expected_contents = '[defaults]\ntest_key = {{ test_variable }}'
        rt expected_contents == contents.strip()
@pytest.fixture()
def collection_artifact(collection_skeleton, tmp_path_factory):