Add dummy DCO workflow to support merge queues

See frequenz-floss/frequenz-sdk-python#363
for more details.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

.github/workflows/dco-merge-queue.yml

@@ -0,0 +1,11 @@
+# Based on https://github.com/hyperledger/besu/pull/5207/files
+name: DCO
+on:
+  merge_group:
+
+jobs:
+  DCO:
+    runs-on: ubuntu-latest
+    if: ${{ github.actor != 'dependabot[bot]' }}
+    steps:
+      - run: echo "This DCO job runs on merge_queue event and doesn't check PR contents"