Enable macOS CI tests (#760)

Author: natecook1000

.github/workflows/pull_request.yml

@@ -25,6 +25,7 @@ jobs:
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
     with:
       windows_exclude_swift_versions: "[{\"swift_version\": \"5.9\"}]"
+      enable_macos_checks: true
 
   cmake-build:
     name: CMake Build