Enable the existing DocC check too, to review its existing failures

Author: stmontgomery

.github/workflows/pull_request.yml

@@ -30,7 +30,7 @@ jobs:
     uses: stmontgomery/github-workflows/.github/workflows/soundness.yml@macos-docs-check
     with:
       license_header_check_project_name: "Swift"
-      docs_check_enabled: false
+      docs_check_enabled: true
       docs_check_macos_enabled: true
       format_check_enabled: false
       api_breakage_check_enabled: false