This change renames tests/sanity.py -> tests/checkers.py.
The term sanity is not very clear and potentially offensive, and it's
already used by `ansible-test sanity` to mean something different.
(cherry picked from commit a986664e99)
Fixes: https://github.com/ansible/ansible-documentation/issues/530
Co-authored-by: Maxwell G <maxwell@gtmx.me>