CompatHelper: bump compat for MetaGraphs in [weakdeps] to 0.8, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the MetaGraphs package from 0.7 to 0.7, 0.8.
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 94.93%. Comparing base (6fe842f) to head (83bd6f3).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
- Coverage   94.94%   94.93%   -0.01%     
==========================================
  Files          14       14              
  Lines        1898     1897       -1     
==========================================
- Hits         1802     1801       -1     
  Misses         96       96              

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