feat(ci) add prune job for stale issues and PRs

[realFlowControl]

Description

This PR adds the https://github.com/actions/stale action to CI to prune issues and PRs that have not seen activity in the recent time.

Reviewer checklist

• Test coverage seems ok.
• Appropriate labels assigned.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 61.74%. Comparing base (0a38276) to head (8366a62).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3388   +/-   ##
=======================================
  Coverage   61.74%   61.74%           
=======================================
  Files         141      141           
  Lines       12481    12481           
  Branches     1630     1630           
=======================================
  Hits         7706     7706           
  Misses       4054     4054           
  Partials      721      721           

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