maybe fixup main coverage diff (#18645)

maybe fixup `main` coverage diff

Author: altendky

.github/workflows/test.yml

@@ -292,7 +292,7 @@ jobs:
       - name: Coverage report (diff)
         if: (github.base_ref != '' || github.event.before != '') && always()
         env:
-          compare-branch: ${{ github.base_ref == '' && steps.parent-commit.hash || format('origin/{0}', github.base_ref) }}
+          compare-branch: ${{ github.base_ref == '' && steps.parent-commit.outputs.hash || format('origin/{0}', github.base_ref) }}
         run: |
           set -o pipefail
           diff-cover --config-file=.diffcover.toml --compare-branch=${{ env.compare-branch }} --fail-under=100 --html-report=coverage-reports/diff-cover.html --markdown-report=coverage-reports/diff-cover.md coverage-reports/coverage.xml | tee coverage-reports/diff-cover-stdout