BUG: better handle optional dependencies for testing

There are a couple of optional dependencies that are seemed to be pulled in for all the test runs and thus we don't notice if a module using it without padding for them not being available. Even if we decide that there are required dependencies, the testing infrastructure needs to be fixed.

E.g:

- pillow is used in `hips2fits` while it could be not available.
- botocore, as reported in https://github.com/astropy/astroquery/issues/3546

Start by reviewing the test dependency configuration and the hips2fits and botocore usage mentioned in the issue. Run tests in an environment without those optional dependencies to identify where they are installed or assumed available. Done means the testing infrastructure exposes missing optional dependencies and affected modules handle their absence.

Written by the indexing model from the issue text.