CompatHelper: bump compat for RDatasets in [extras] to 0.8, (keep existing compat)

[github-actions]

This pull request changes the compat entry for the RDatasets package from 0.7.7 to 0.7.7, 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 100.00%. Comparing base (864a55a) to head (86fead4).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #46   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            6         6           
  Lines          126       126           
=========================================
  Hits           126       126           

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