Merge pull request kubernetes-sigs#12034 from Okabe-Junya/fix-12010

🌱 Use github.base_ref in markdown-link-check

Author: k8s-ci-robot

.github/workflows/pr-md-link-check.yaml

@@ -20,4 +20,4 @@ jobs:
         use-quiet-mode: 'yes'
         config-file: .markdownlinkcheck.json
         check-modified-files-only: 'yes'
-        base-branch: main
+        base-branch: ${{ github.base_ref }}

docs/release/role-handbooks/ci-signal/README.md

@@ -45,7 +45,6 @@ While we add test coverage for the new release branch we will also drop the test
   TEST_INFRA_DIR=../../k8s.io/test-infra make generate-test-infra-prowjobs
   ```
 6. Verify the jobs and dashboards a day later by taking a look at: `https://testgrid.k8s.io/sig-cluster-lifecycle-cluster-api-1.8`
-7. Update the [PR markdown link checker](https://github.com/kubernetes-sigs/cluster-api/blob/main/.github/workflows/pr-md-link-check.yaml) accordingly (e.g. `main` -> `release-1.8`).
 
 Prior art: