chore: Switch pytest

[mrbazzan]

Description

• remove unused base.txt file
• switch to pytest
• update test requirements

Checklist

• I have opened this pull request against master
• I have added or modified the tests when changing logic
• I have followed the conventional commits guidelines to add meaningful information into the changelog
• I have read the contribution guidelines and I have joined #workgroup-pr-review on
  Slack to find a “pr review buddy” who is going to review my pull request.

[mrbazzan]

@fsbraun
I wanted to omit the coverage for djangocms/migrations/* but
some of the migration files were manually written e.g 0006_migrate_to_filer.py.
How do I find the test(file|function) which "covers" this migration?

[fsbraun]

I doubt there is any. It just runs (if it is covered).

[fsbraun]

Looks great! I don't wory about the missing migration coverage.