[CI] Add support for GitHub Actions

I have disabled all checks that are currently failing for now to get the initial support in. I will work on enabling these tests in follow-up PRs one-by-one.

Author: ahoppen

.github/workflows/pull_request.yml

@@ -0,0 +1,30 @@
+name: Pull request
+
+on:
+  pull_request:
+    types: [opened, reopened, synchronize]
+
+jobs:
+  tests:
+    name: Test
+    uses: swiftlang/github-workflows/.github/workflows/swift_package_test.yml@main
+    with:
+      # https://github.com/swiftlang/swift-syntax/issues/2992
+      enable_windows_checks: false
+  soundness:
+    name: Soundness
+    uses: swiftlang/github-workflows/.github/workflows/soundness.yml@main
+    with:
+      license_header_check_project_name: "Swift.org"
+      # https://github.com/swiftlang/swift-syntax/issues/2986
+      api_breakage_check_enabled: false
+      # https://github.com/swiftlang/swift-syntax/issues/2987
+      docs_check_enabled: false
+      # https://github.com/swiftlang/swift-syntax/issues/2988
+      format_check_enabled: false
+      # https://github.com/swiftlang/swift-syntax/issues/2989
+      license_header_check_enabled: false
+      # https://github.com/swiftlang/swift-syntax/issues/2990
+      unacceptable_language_check_enabled: false
+      # https://github.com/swiftlang/swift-syntax/issues/2991
+      yamllint_check_enabled: false