Use apt-get to install towncrier

[johannaengland]

Scope and purpose

This has become necessary due to PEP 668.

Our test workflows are safe (for now), since we test on Python versions 3.9-3.11.

Contributor Checklist

Every pull request should have this checklist filled out, no matter how small it is. More information about contributing to Zino can be found in the README.

• [ ] Added a changelog fragment for towncrier
  • workflow change
• [ ] Added/amended tests for new/changed code
• [ ] Added/changed documentation
• [X] Linted/formatted the code with black, ruff and isort, easiest by using pre-commit
• [X] The first line of the commit message continues the sentence "If applied, this commit will ...", starts with a capital letter, does not end with punctuation and is 50 characters or less long. See https://cbea.ms/git-commit/
• [ ] If applicable: Created new issues if this PR does not fix the issue completely/there is further work to be done

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 98.66%. Comparing base (6dc98ef) to head (7b96eb0). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #373 +/- ## ======================================= Coverage 98.66% 98.66% ======================================= Files 77 77 Lines 9711 9711 ======================================= Hits 9581 9581 Misses 130 130 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud