GHA: Add PR dependency check (#9671)

Add a workflow that will check if dependent PR are merged. If not, fail
the build.

Depends on: swiftlang/github-workflows/pull/233

Author: bkhouri

.github/workflows/pull_request_dependency_check.yaml

@@ -0,0 +1,11 @@
+on:
+  pull_request_target:
+    types: [opened, edited, reopened, labeled, unlabeled, synchronize]
+
+permissions:
+  issues: read
+  pull-requests: read
+
+jobs:
+  check_dependencies:
+    uses: swiftlang/github-workflows/.github/workflows/github_actions_dependencies.yml@main