CompatHelper: bump compat for Symbolics to 6, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Symbolics package from 5 to 5, 6.
This keeps the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 47.38%. Comparing base (ad4c6b2) to head (410f488).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #12   +/-   ##
=======================================
  Coverage   47.38%   47.38%           
=======================================
  Files          13       13           
  Lines         249      249           
=======================================
  Hits          118      118           
  Misses        131      131           

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