Add workflow to check mergeable state executed on pull request

.github/workflows/check_if_branch_is_mergeable.yml

@@ -0,0 +1,40 @@
+name: mergeable
+
+on:
+  pull_request:
+    branches: [main]
+  push:
+    branches: [main]
+
+jobs:
+  is_mergeable:
+    runs-on:
+      labels: depot-ubuntu-22.04-8
+      group: public-depot
+    timeout-minutes: 15
+    steps:
+      - name: 🛎️ Checkout main
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: ${{ env.FETCH_DEPTH }}
+          ref: main
+      - name : Store main sha in context
+        run: echo "main_sha=$(git rev-parse main)" >> "${GITHUB_ENV}"
+      - name: Calculate depth
+        run: echo "FETCH_DEPTH=$(( ${{ github.event.pull_request.commits }} + 1 ))" >> "${GITHUB_ENV}"
+      - name: 🛎️ Checkout branch with all history
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: ${{ env.FETCH_DEPTH }}
+          ref: ${{ github.event.pull_request.head.sha }}
+      - name: Check and store mergable state
+        id: mergeable_check
+        run: |
+          echo "Check if main is ancestor of ${{ github.event.pull_request.head.sha }} (branch HEAD)";
+          if $(git merge-base --is-ancestor ${{ env.main_sha }} ${{ github.event.pull_request.head.sha }}); then
+            echo "Branch is mergeable";
+            exit 0;
+          else
+            echo "Branch needs to be updated";
+            exit 1;
+          fi