update the CI to only run on nightly-main

Author: shahmishal

.github/workflows/pull_request.yml

@@ -9,8 +9,8 @@ jobs:
     name: Test
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
     with:
-      linux_exclude_swift_versions: '[{"swift_version": "5.9"}, {"swift_version": "5.10"}]'
-      windows_exclude_swift_versions: '[{"swift_version": "5.9"}]'
+      linux_swift_versions: '["nightly-main"]'
+      windows_swift_versions: '["nightly-main"]'
 
   soundness:
     name: Soundness