Fix downgrade path for 2.18.0

[svenklemm]

This patch adjusts the downgrade script generation to not include
incompatible files from the 2.18.0 release that would break script
generation and replaces them with a working version. This adjustment
can be removed after we release of 2.18.1.
This patch also reenables the downgrade test.

Disable-check: force-changelog-file
Disable-check: approval-count

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.28%. Comparing base (59f50f2) to head (c00ba1d).
Report is 719 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7620      +/-   ##
==========================================
+ Coverage   80.06%   81.28%   +1.21%     
==========================================
  Files         190      240      +50     
  Lines       37181    44700    +7519     
  Branches     9450    11159    +1709     
==========================================
+ Hits        29770    36335    +6565     
- Misses       2997     3976     +979     
+ Partials     4414     4389      -25     

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