comparing level 19 to level 22 and expecting a stricter better result from level 22
is not that guaranteed,
because level 19 and 22 are very close to each other,
especially for small files,
so any noise in the final compression result
result in failing this test.
Level 22 could be compared to something much lower, like level 15,
But level 19 is required anyway, because there is a clamping test which depends on it.
Removed level 22, kept level 19
Add cli-tests to `make test`. This adds a `python3` dependency to `make
test`, but not `make check`. We could make this dependency optional by
skipping the tests if `python3` is not present.
