CompatHelper: bump compat for Symbolics to 7, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the Symbolics package from 5, 6, 7.1 to 5, 6, 7.1, 7.
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-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 40.08%. Comparing base (88934bf) to head (e3f8fab).
⚠️ Report is 1 commits behind head on main.

❗ There is a different number of reports uploaded between BASE (88934bf) and HEAD (e3f8fab). Click for more details.

HEAD has 1 upload less than BASE

Flag	BASE (88934bf)	HEAD (e3f8fab)
	2	1

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #197      +/-   ##
==========================================
- Coverage   48.14%   40.08%   -8.07%     
==========================================
  Files          20       20              
  Lines       12634    12525     -109     
==========================================
- Hits         6083     5021    -1062     
- Misses       6551     7504     +953     

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