Pin workflows to a specific version

Pin the workflows to a specific version to ensure stability and
consistency across runs.

Author: bkhouri

.github/workflows/pull_request.yml

@@ -25,7 +25,7 @@ jobs:
 
   tests:
     name: Test
-    uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
+    uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@0.0.3
     with:
       windows_exclude_swift_versions: "[{\"swift_version\": \"5.9\"}]"
       enable_macos_checks: true
@@ -58,6 +58,6 @@ jobs:
 
   soundness:
     name: Soundness
-    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@0.0.3
     with:
       shell_check_enabled: false  # bug: https://github.com/apple/swift-argument-parser/issues/703