deploy(link-check): verify absolute git-scm.com links also in forks

When deploying in forks, the base URL is distinctly different from
https://git-scm.com. But there are plenty of such links in the HTML
pages, e.g. all of those links in the ProGit book that point to Git's
homepage. Let's include those in the checks so that broken links are
noticed earlier rather than later.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

.github/actions/deploy-to-github-pages/action.yml

@@ -138,6 +138,9 @@ runs:
         echo "remap-dotdot=$(echo "$base_url" |
           sed -n 's|^\(https\?:\/\/.*\)\(/git-scm\.com\)$|--remap '\''^(\1.*) file://../$1'\''|p')" \
           >>$GITHUB_OUTPUT
+        # When running in forks, do treat https://git-scm.com links as if they were relative
+        test https://git-scm.com = "$base_url" ||
+        echo "remap-git-scm=--remap '^https?://git-scm.com(.*) file://$PWD/public\$1'" >>$GITHUB_OUTPUT
 
     - name: check for downgrades to unencrypted HTTP
       if: startsWith(env.base_url, 'https://')
@@ -163,6 +166,7 @@ runs:
           --base '${{ env.base_url }}'
           --remap '${{ steps.remap.outputs.result }}'
           ${{ steps.remap.outputs.remap-dotdot }}
+          ${{ steps.remap.outputs.remap-git-scm }}
           --exclude file:///path/to/repo.git/
           --exclude file:///caminho/para/o/reposit%C3%B3rio.git/
           --exclude file:///ruta/a/repositorio.git/