chore(workflows): add close-issue-reason for stale bot

[juliapampus]

What this PR changes/adds

Adds close-issue-reason to close stale issues as "not planned" by default.

Why it does that

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Further notes

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Linked Issue(s)

Closes #1947

Checklist

• added appropriate tests?
• performed checkstyle check locally?
• added/updated copyright headers?
• documented public classes/methods?
• added/updated relevant documentation?
• assigned appropriate label? (exclude from changelog with label no-changelog)
• formatted title correctly? (take a look at the CONTRIBUTING and styleguide for details)

[codecov-commenter]

Codecov Report

Merging #1948 (2c0ed16) into main (23a4d24) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #1948   +/-   ##
=======================================
  Coverage   62.78%   62.78%           
=======================================
  Files         781      781           
  Lines       16608    16608           
  Branches     1080     1080           
=======================================
  Hits        10428    10428           
  Misses       5729     5729           
  Partials      451      451           

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