[GHA] Update to the latest workflows

# Motivation

I made more progress on the reusable workflows in NIO so it's even easier to adopt them.

# Modification

This PR fixes up the renamed workflow references and adds unit tests and cxx-interop checks.

# Result

Green GH actions CI

Author: FranzBusch

.github/workflows/pull_request.yml

@@ -1,14 +1,27 @@
 name: Pull Request
 
 on:
-  pull_request:
-    types: [opened, reopened, synchronize, ready_for_review]
- 
+    pull_request:
+      types: [opened, reopened, synchronize]
+
 jobs:
-  call-reusable-pull-request-workflow:
-    name: Checks
-    uses: apple/swift-nio/.github/workflows/reusable_pull_request.yml@main
-    with:
-      benchmarks_linux_enabled: false
-      unacceptable_language_check_enabled: false
-      license_header_check_project_name: "SwiftOpenAPIGenerator"
+    soundness:
+        name: Soundness
+        uses: apple/swift-nio/.github/workflows/soundness.yml@main
+        with:
+            license_header_check_project_name: "SwiftOpenAPIGenerator"
+            unacceptable_language_check_enabled: false
+
+    unit-tests:
+        name: Checks
+        uses: apple/swift-nio/.github/workflows/unit_tests.yml@main
+        with:
+            linux_5_8_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_5_9_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_5_10_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_nightly_6_0_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+            linux_nightly_main_arguments_override: "-Xswiftc -warnings-as-errors --explicit-target-dependency-import-check error"
+
+    cxx-interop:
+        name: Checks
+        uses: apple/swift-nio/.github/workflows/cxx_interop.yml@main