### Summary

I know there is some ongoing work to mitigate these problems, but since I'm not aware which parts have already been addressed and which not, I want to share some common failures here which I've seen during the last days:

1. When running `ansible-test sanity --color -v --junit --coverage-check --changed --docker --base-branch origin/main --skip-test pylint --skip-test ansible-doc --skip-test validate-modules --allow-disabled` in CI, the Python 2.6 `import` test fails:
```
02:05 ERROR: Command "/root/ansible_collections/community/general/tests/output/.tmp/sanity/import/minimal-py26/bin/python /root/ansible/test/lib/ansible_test/_data/quiet_pip.py install --disable-pip-version-check coverage -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt" returned exit status 1.
02:05 >>> Standard Error
02:05 Could not find a version that satisfies the requirement coverage<5.0.0,>=4.5.1 (from -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt (line 2)) (from versions: )
02:05 No matching distribution found for coverage<5.0.0,>=4.5.1 (from -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt (line 2))
02:05 >>> Standard Output
02:05 Collecting coverage<5.0.0,>=4.5.1 (from -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt (line 2))
```
(See https://app.shippable.com/github/ansible-collections/community.general/runs/8257/1/console for the full log)

2. When running unit tests for Python 2.6 with `ansible-test units -v --color --docker --coverage` with `unittest2 ; python_version < '2.7'` in tests/unit/requirements.txt, it fails:
```
Run command: /usr/bin/python2.6 /root/ansible/test/lib/ansible_test/_data/quiet_pip.py install --disable-pip-version-check -r /root/ansible/test/lib/ansible_test/_data/requirements/units.txt -r tests/unit/requirements.txt coverage -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt
Collecting unittest2 (from -r tests/unit/requirements.txt (line 1))
  Could not find a version that satisfies the requirement unittest2 (from -r tests/unit/requirements.txt (line 1)) (from versions: )
No matching distribution found for unittest2 (from -r tests/unit/requirements.txt (line 1))
ERROR: Command "/usr/bin/python2.6 /root/ansible/test/lib/ansible_test/_data/quiet_pip.py install --disable-pip-version-check -r /root/ansible/test/lib/ansible_test/_data/requirements/units.txt -r tests/unit/requirements.txt coverage -c /root/ansible/test/lib/ansible_test/_data/requirements/constraints.txt" returned exit status 1.
```
(See https://github.com/ansible-collections/community.hrobot/runs/2264772861?check_suite_focus=true)


### Issue Type

Bug Report

### Component Name

ansible-test

### Ansible Version

```console (paste below)
devel
```


### Configuration

...

### OS / Environment

...

### Steps to Reproduce

...

### Expected Results

...

### Actual Results

...
if command == 'sanity' and data_context().content.is_ansible:
        requirements = os.path.join(data_context().content.sanity_path, 'code-smell', '%s.requirements.txt' % context)
        if os.path.exists(requirements) and os.path.getsize(requirements):
            options += ['-r', requirements]
    if command == 'units':
        requirements = os.path.join(data_context().content.unit_path, 'requirements.txt')
        if os.path.exists(requirements) and os.path.getsize(requirements):
            options += ['-r', requirements]
        content_constraints = os.path.join(data_context().content.unit_path, 'constraints.txt')
    if command in ('integration', 'windows-integration', 'network-integration'):
        requirements = os.path.join(data_context().content.integration_path, 'requirements.txt')
        if os.path.exists(requirements) and os.path.getsize(requirements):
            options += ['-r', requirements]
        requirements = os.path.join(data_context().content.integration_path, '%s.requirements.txt' % command)
        if os.path.exists(requirements) and os.path.getsize(requirements):
            options += ['-r', requirements]
        content_constraints = os.path.join(data_context().content.integration_path, 'constraints.txt')
    if command.startswith('integration.cloud.'):
        content_constraints = os.path.join(data_context().content.integration_path, 'constraints.txt')
    if packages:
        options += packages
    if not options:
        return None
    if use_constraints:
        if content_constraints and os.path.exists(content_constraints) and os.path.getsize(content_constraints):
            
            options.extend(['-c', content_constraints])
        options.extend(['-c', constraints])
    return pip + ['install', '--disable-pip-version-check'] + options
def command_shell(args):