CompatHelper: bump compat for GraphViz in [weakdeps] to 0.3, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the GraphViz package from 0.2 to 0.2, 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 90.72%. Comparing base (4cc7c6c) to head (cd9e6df).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #332   +/-   ##
=======================================
  Coverage   90.72%   90.72%           
=======================================
  Files          16       16           
  Lines        2263     2263           
=======================================
  Hits         2053     2053           
  Misses        210      210           

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