### 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

...
"""
    :type parser: argparse.ArgumentParser
    """
    parser.add_argument('--lint',
                        action='store_true',
                        help='write lint output to stdout, everything else stderr')
    parser.add_argument('--junit',
                        action='store_true',
                        help='write test failures to junit xml files')
    parser.add_argument('--failure-ok',
                        action='store_true',
                        help='exit successfully on failed tests after saving results')
def add_changes(parser, argparse):
    """
    :type parser: argparse.ArgumentParser
    :type argparse: argparse
    """
    parser.add_argument('--changed', action='store_true', help='limit targets based on changes')
    changes = parser.add_argument_group(title='change detection arguments')
    changes.add_argument('--tracked', action='store_true', help=argparse.SUPPRESS)
    changes.add_argument('--untracked', action='store_true', help='include untracked files')
    changes.add_argument('--ignore-committed', dest='committed', action='store_false', help='exclude committed files')
    changes.add_argument('--ignore-staged', dest='staged', action='store_false', help='exclude staged files')
    changes.add_argument('--ignore-unstaged', dest='unstaged', action='store_false', help='exclude unstaged files')
    changes.add_argument('--changed-from', metavar='PATH', help=argparse.SUPPRESS)
    changes.add_argument('--changed-path', metavar='PATH', action='append', help=argparse.SUPPRESS)
def add_environments(parser, isolated_delegation=True):