Use the base branch SHA for GitHub action.

When running our GitHub action, let's try to use the base SHA for the target branch instead of the base SHA for the PR branch.

Author: markafoltz

.github/workflows/auto-publish.yml

@@ -9,10 +9,12 @@ jobs:
     runs-on: ubuntu-20.04
     steps:
       - uses: actions/checkout@v2
+        with:
+          ref: "${{ github.event.pull_request.base.sha }}"
       - uses: w3c/spec-prod@v2
         with:
           GH_PAGES_BRANCH: gh-pages
           W3C_ECHIDNA_TOKEN: ${{ secrets.ECHIDNA_TOKEN }}
           W3C_WG_DECISION_URL: https://lists.w3.org/Archives/Public/public-secondscreen/2022Apr/0007.html
           W3C_BUILD_OVERRIDE: |
-            specStatus: CRD
+            specStatus: CRD