[INFRA] Remove changelog generator CI workflow

[effigies]

This hasn't been working for a while. The new method is:

$ export GITHUB_TOKEN=...  # You need a GitHub token with permissions to read public repos
$ uv run tools/make_changelog.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.71%. Comparing base (8fd451a) to head (fca5ac9).
⚠️ Report is 94 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2196   +/-   ##
=======================================
  Coverage   82.71%   82.71%           
=======================================
  Files          20       20           
  Lines        1608     1608           
=======================================
  Hits         1330     1330           
  Misses        278      278           

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