Update docs workflow version

There was a intermediate state where we needed this branch, but we don't anymore.

Author: pedro-psb

.github/workflows/pr-checks.yml

@@ -7,9 +7,9 @@ on:
 jobs:
   docs:
     # The workflow tag and the pulpdocs_ref must match.
-    uses: 'pulp/pulp-docs/.github/workflows/docs-ci.yml@rewrite-as-mkdocs-plugin'
+    uses: 'pulp/pulp-docs/.github/workflows/docs-ci.yml@main'
     with:
-      pulpdocs_ref: 'rewrite-as-mkdocs-plugin'
+      pulpdocs_ref: 'main'
 
   pr-checks:
     runs-on: ubuntu-latest