codecov: allow coverage offsets for more base commit flexibility (spa…

…ck#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

.codecov.yml

@@ -19,3 +19,16 @@ comment: off
 # annotations in files that seemingly have nothing to do with the PR.
 github_checks:
     annotations: false
+
+# 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.
+#
+# 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
+codecov:
+  allow_coverage_offsets: true