ci: Use soundness workflow from swiftlang/github-workflows (#648)

This moves to the reusable soundness workflow in the swiftlang
organization.

.github/workflows/pull_request.yml

@@ -7,7 +7,7 @@ on:
 jobs:
     soundness:
         name: Soundness
-        uses: apple/swift-nio/.github/workflows/soundness.yml@main
+        uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
         with:
             api_breakage_check_enabled: false
             broken_symlink_check_enabled: true
@@ -17,6 +17,7 @@ jobs:
             license_header_check_project_name: "SwiftOpenAPIGenerator"
             shell_check_enabled: true
             unacceptable_language_check_enabled: true
+            yamllint_enabled: false
 
     unit-tests:
         name: Unit tests