CI: check for pending releases

[fingolfin]

This adds a weekly workflow using check-pending-release. It opens a single issue (label pending release) when there are commits since the last release that have been left untouched for at least 7 days, so finished work does not go unreleased. Changes to .github and .gitignore do not count. The issue is closed once a release is made; the job added to release.yml makes that happen right after a release made with the release workflow.

See the action's README for details and options, such as the quiet period or ignored paths.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.73%. Comparing base (c93e2a0) to head (5a2e93f).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #26   +/-   ##
=======================================
  Coverage   91.73%   91.73%           
=======================================
  Files          15       15           
  Lines        1537     1537           
=======================================
  Hits         1410     1410           
  Misses        127      127           

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