CompatHelper: bump compat for LinearSolve to 3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the LinearSolve package from ~2.39.0 to ~2.39.0, 3.
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 88.18%. Comparing base (4baba0c) to head (b4b1e89).
Report is 43 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #174   +/-   ##
=======================================
  Coverage   88.18%   88.18%           
=======================================
  Files           8        8           
  Lines        1710     1710           
=======================================
  Hits         1508     1508           
  Misses        202      202           

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[ufechner7]

Done manually.