At least temporarily, if anyone wants to make it working in the future
(I am not motivated enough as we use vcs-diff-lint/python for similar
things).

Mostly wrong import order, useless imports, etc.

- Requires us to add pytest.ini to tell pytest where to look for test
  files, and set the python path.
- Mock drops terminal from the tested code, so we have to "mock" it in
  test_colors()
- Enable coverage in tox tests.

- Some tests can not work at rpmbuild time, because we can not run
  rpmbuild in rpmbuild, and there's no .git/ directory, skip.
- Use 'titodir' below 'srcdir', to not pollute the /tmp/tito dir.
- The test_colors() test requires color-friendly TERM env.
- EL7 is EOL, do not enable tests there.

The Version is more strict, but we only use this for the implementation
of tito.props configuration:

    [requirements]
    tito = <version>

And the tito versions are not anyhow extraordinary.

Note, this is done to fix a tox test failure.

Even Python 2.7 is now EOL.  And this weird import has been breaking
the Tox tests (importing the tagger class brought in other unnecessary
deps and tests bombed).

This is tricky.  Note the sys.path hack in test/unit/__init__.py where
we intentionally use the Fedora's default Python libraries with a
different Python version selected by Tox.  Right now it means that we
use, e.g., python3-rpm compiled for Python 3.12 (F39) with Python 3.7
(which probably works because Tox is executed as root in the tox
container, overwriting the pre-compiled *.pyc files in container).

Some tests need to be skipped in Tox, therefore the skip_if_tox()
method.

Also, the GitHub's action for 'git checkout' provides somewhat
non-standard environment for Tito to work, hence the fix_tox_env()
configuration method.