Adjust CI so gfortran 10 tests run

[andrewwinters5000]

The gfortran-10 compiler is available in ubuntu-22.04 and no longer in ubuntu-latest. See (actions/runner-images#10636).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.83%. Comparing base (b05419c) to head (a1c7839).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #128   +/-   ##
=======================================
  Coverage   75.83%   75.83%           
=======================================
  Files          68       68           
  Lines       10568    10568           
  Branches        2        2           
=======================================
  Hits         8014     8014           
  Misses       2554     2554           

Flag	Coverage Δ
unittests	75.83% <ø> (ø)

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