codecov: allow coverage offsets for more base commit flexibility (#25293)
codecov: allow coverage offsets for more base commit flexibility (#25293)

This is an attempt to fix "Missing base commit" messages in the codecov UI. Because we do not run
full tests on package PRs, package PRs' merge commits on `develop` don't have coverage info. It
appears that codecov will give you an error if the pseudo-base's coverage data doesn't all apply
properly to the real PR base, unless the `allow_coverage_offsets` option is set.

* See here for docs:
  https://docs.codecov.com/docs/comparing-commits#pseudo-comparison

* See here for another potential solution:
  https://community.codecov.com/t/2480/15
LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack,LLNL/spack