github: workflows: add developer sign-off validation workflow

.github/workflows/dco.yml

@@ -0,0 +1,32 @@
+# SPDX-FileCopyrightText: Copyright The Zephyr Project Contributors
+# SPDX-License-Identifier: Apache-2.0
+
+name: DCO Check
+
+on: [pull_request]
+
+permissions:
+  contents: read
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  dco-check:
+    name: Check developer sign-off
+    runs-on: ubuntu-24.04
+    # The sign-off check for dependabot should be skipped
+    if: github.actor != 'dependabot[bot]'
+    steps:
+      - name: Checkout
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          # Full history and the PR head so the action can resolve the base
+          # branch and merge-base (see actions/checkout#552).
+          fetch-depth: 0
+          ref: ${{ github.event.pull_request.head.sha }}
+          persist-credentials: false
+
+      - name: Check commit sign-off
+        uses: zephyrproject-rtos/action-dco@e3485a11e085fdc05fa4320e9cc3a86ccd665d89 # v1.0.0