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
• Linted/formatted the code with black, ruff and isort, easiest by using pre-commit
• 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]

Codecov Report

All modified and coverable lines are covered by tests ✅

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

Additional details and impacted files

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

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[sonarcloud]

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