no nightly checks for macOS

Author: ktoso

.github/workflows/pull_request.yml

@@ -185,7 +185,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        swift_version: ['6.1.2', 'nightly']
+        swift_version: ['6.1.2']  # no nightly checks for macOS
         os_version: ['macos']
         jdk_vendor: ['corretto']
         sample_app: [  # TODO: use a reusable-workflow to generate those names