Update release-plan workflows.

[kategengler]

Used kategengler/create-release-plan#kg-reusable-actions (PR'd to create-release-plan)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.54%. Comparing base (e0d196e) to head (698b970).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1085   +/-   ##
=======================================
  Coverage   95.54%   95.54%           
=======================================
  Files          21       21           
  Lines         516      516           
=======================================
  Hits          493      493           
  Misses         23       23           

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[kategengler]

I proposed the extraction to actions in create-release-plan-setup here release-plan/create-release-plan-setup#200

For now these actions are under one of my repos but they are tagged so there is no risk to using them as-is even before they are moved to a more shared repo.