Don’t exclude 5.8 in PR testing

Swift 5.8 was removed from the underlying workflow in swiftlang/github-workflows#107

Author: ahoppen

.github/workflows/pull_request.yml

@@ -8,8 +8,6 @@ jobs:
   tests:
     name: Test
     uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
-    with:
-      linux_exclude_swift_versions: "[{\"swift_version\": \"5.8\"}]"
   soundness:
     name: Soundness
     uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main