Skip towncrier check on 'nonews' label

[johannaengland]

Scope and purpose

This also changes that the check runs when a label is added/removed and on the default actions: when a PR is opened/reopened or the PR's head branch is updated.

It's fitting - this PR will also be right away used as test

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
• 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

[sonarqubecloud]

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 SonarQube Cloud

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.66%. Comparing base (b9665d3) to head (fc836cb).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #388   +/-   ##
=======================================
  Coverage   98.66%   98.66%           
=======================================
  Files          77       77           
  Lines        9711     9711           
=======================================
  Hits         9581     9581           
  Misses        130      130           

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