Add missing script

.github/workflows/scripts/validate-commit-in-head.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+if [[ -z "${GIT_COMMIT:-}" ]]; then
+  echo "Error: Environment variable GIT_COMMIT is required"
+  exit 1
+fi
+
+if git merge-base --is-ancestor "$GIT_COMMIT" HEAD; then
+  echo "Commit $GIT_COMMIT is contained in HEAD"
+else
+  echo "Error: Commit $GIT_COMMIT is not contained in HEAD"
+  exit 1
+fi