Introduce some integration tests for the template

[drewoldag]

Currently there is a GitHub action that will hydrate two test projects (one uses the default responses to the questions, the other provides some non-default responses)

However, those tests were introduced before the template allowed the user to make branching choices (i.e. black vs. pylint) that result in different files or file content.

It would be nice to be able to confirm via something like integration or unit tests that the various responses result in a hydrated test projects that contain the correct files or file contents.

[olivialynn]

ci.yml has been updated to provide some testing for non-default options. Some remaining issues/things to think about:

• No flags are specified in the default run.
  • This can make conditioning weird: eg, pylint's step needing if: ${{ contains (matrix.copier_config.name, 'Base') }} to check that we wanted pylint in this run.
• Some questions have more than two options: eg, mypy_type_checking has none, basic, and strict.
  • We currently only check the first non-default option; do we want to exhaustively check each option?
  • Do we care which combinations are present (eg, pylint + BSD license + lfs disabled but also pylint + no license + lfs enabled), or is it sufficient to make sure we check each option at least once?
• This does not technically do any checks that the options have worked as intended, beyond implicit assumptions like "we can only run the pytests on a module that has, in fact, been made" or "we can only run a pylint check if the options we picked lead us to actually install it."

[drewoldag]

Related to #190

[drewoldag]

Won't be doing this now.