CI: drastically reduce the number of tests for package only PRs (#22410)

PRs that change only package recipes will only run tests under "package_sanity.py" and without coverage. This should result in a huge drop the cpu-time spent in CI for most PRs.

.github/workflows/unit_tests.yaml

@@ -332,7 +332,7 @@ jobs:
           coverage xml
         else
           echo "ONLY PACKAGE RECIPES CHANGED [skipping coverage]"
-          $(which spack) unit-test -x -m "not maybeslow"
+          $(which spack) unit-test -x -m "not maybeslow" -k "package_sanity"
         fi
     - uses: codecov/codecov-action@v1
       if: ${{ needs.changes.outputs.with_coverage == 'true' }}

share/spack/qa/run-unit-tests

@@ -44,7 +44,7 @@ spack -p --lines 20 spec mpileaks%gcc ^elfutils@0.170
 #-----------------------------------------------------------
 if [[ "$ONLY_PACKAGES" == "true" ]]; then
   echo "ONLY PACKAGE RECIPES CHANGED [skipping slow unit tests]"
-  export PYTEST_ADDOPTS='-m "not maybeslow"'
+  export PYTEST_ADDOPTS='-k "package_sanity" -m "not maybeslow"'
 fi
 
 $coverage_run $(which spack) unit-test -x --verbose