Fix terminology: deployment branch policies, not branch protection rules (#129)

Caught by Copilot review on the docs-playbook PR documenting this
behavior. "Branch protection rules" names a different, unrelated
repo-level GitHub feature (PR requirements, required status checks) -
what actually restricts which branches/tags can use an environment is
called deployment branch policies.

Author: recrwplay

.github/workflows/reusable-docs-build.yml

@@ -131,10 +131,10 @@ jobs:
     outputs:
       pages-listed: ${{ steps.page-list-artifact.outcome }}
 
-    # Only scope to an environment (and its branch protection rules) for actual
+    # Only scope to an environment (and its deployment branch policies) for actual
     # publish builds, which are the only ones that need DOCS_PUBLISH_URL. Ordinary
     # preview builds (e.g. PR checks) don't need it and shouldn't be blocked by
-    # environment branch-protection rules meant for publishing.
+    # environment deployment branch policies meant for publishing.
     environment:
       name: ${{ inputs.package-script == 'verify:publish' && inputs.publish-env || '' }}
       deployment: false