### Summary

See: https://github.com/ansible/ansible/blob/devel/lib/ansible/modules/git.py#L760 :

```py
            repo_path = os.path.join(repo_path.split('.git')[0], gitdir)
```

the intention of this code seems to be to strip `.git` from the end of the path.

If the repo path contains `.git` anywhere, like `/tmp/music.gittern/myrepo`, tasks will unexpectedly fail:

```
fatal: [localhost]: FAILED! => {"changed": false, "details": "/tmp/music/../.git/modules/submodule is not a directory", "msg": "Current repo does not have a valid reference to a separate Git dir or it refers to the invalid path"}
```

For a playbook like:
```yaml
---
- hosts: localhost
  tasks:
   - name: test git
     git: 
        repo: ...
        dest: /tmp/music.gittern/myrepo/submodule
```

I can't tell if this is a potential security issue or just an unexpected corner case. What I am pretty sure I can tell, is that that's not how one strips `.git` from the end of a path.

### Issue Type

Bug Report

### Component Name

git

### Ansible Version

```console
$ ansible --version
2.11
```


### Configuration

```console
$ ansible-config dump --only-changed
ANSIBLE_NOCOWS(/home/enrico/dev/transilience/ansible.cfg) = True
```


### OS / Environment

Debian Bullseye

### Steps to Reproduce

Use submodules in a repo whose path contains `.git` anywhere as part of a file name.
For example:
```yaml
---
- hosts: localhost
  tasks:
   - name: test git
     git: 
        repo: ...
        dest: /tmp/music.gittern/myrepo/submodule
```

### Expected Results

I'd expect directory names like `gato.gito` not to be interpreted specially by mistake

### Actual Results

```console
fatal: [localhost]: FAILED! => {"changed": false, "details": "/tmp/music/../.git/modules/submodule is not a directory", "msg": "Current repo does not have a valid reference to a separate Git dir or it refers to the invalid path"}
```


### Code of Conduct

- [X] I agree to follow the Ansible Code of Conduct
import os
import re
import shlex
import stat
import sys
import shutil
import tempfile
from ansible.module_utils.compat.version import LooseVersion
from ansible.module_utils._text import to_native, to_text
from ansible.module_utils.basic import AnsibleModule
from ansible.module_utils.common.locale import get_best_parsable_locale
from ansible.module_utils.common.process import get_bin_path
from ansible.module_utils.six import b, string_types
def relocate_repo(module, result, repo_dir, old_repo_dir, worktree_dir):
    if os.path.exists(repo_dir):
        module.fail_json(msg='Separate-git-dir path %s already exists.' % repo_dir)
    if worktree_dir:
        dot_git_file_path = os.path.join(worktree_dir, '.git')
        try:
            shutil.move(old_repo_dir, repo_dir)
            with open(dot_git_file_path, 'w') as dot_git_file:
                dot_git_file.write('gitdir: %s' % repo_dir)
            result['git_dir_before'] = old_repo_dir
            result['git_dir_now'] = repo_dir
        except (IOError, OSError) as err:
            
            if os.path.exists(repo_dir):
                shutil.move(repo_dir, old_repo_dir)
            module.fail_json(msg=u'Unable to move git dir. %s' % to_text(err))
def head_splitter(headfile, remote, module=None, fail_on_error=False):