Enforce CHANGELOG.md updates in PRs

[LanderOtto]

This commit adds a new Continuous Integration check to ensure that CHANGELOG.md is updated in every pull request before it can be merged into the master branch.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 64.15%. Comparing base (1dceee5) to head (c81a029).
⚠️ Report is 1 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1066   +/-   ##
=======================================
  Coverage   64.14%   64.15%           
=======================================
  Files          93       93           
  Lines       17509    17510    +1     
  Branches     2150     2149    -1     
=======================================
+ Hits        11232    11234    +2     
+ Misses       6000     5997    -3     
- Partials      277      279    +2     

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