[DNM, WIP] Introduce a macOS DocC soundness check

Author: stmontgomery

.github/workflows/pull_request.yml

@@ -27,9 +27,10 @@ jobs:
       enable_android_sdk_build: true
   soundness:
     name: Soundness
-    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@0.0.3
+    uses: stmontgomery/github-workflows/.github/workflows/soundness.yml@macos-docs-check
     with:
       license_header_check_project_name: "Swift"
       docs_check_enabled: false
+      docs_check_macos_enabled: true
       format_check_enabled: false
       api_breakage_check_enabled: false