Add workflow job to label PRs with conflicts (#303)

.github/workflows/label-conflicts.yml

@@ -0,0 +1,28 @@
+name: "Label merge conflicts"
+on:
+  # So that PRs touching the same files as the push are updated
+  push:
+  # So that the `dirtyLabel` is removed if conflicts are resolve
+  # We recommend `pull_request_target` so that github secrets are available.
+  # In `pull_request` we wouldn't be able to change labels of fork PRs
+  pull_request_target:
+    # GitHub documents "synchronize" as:
+    # A pull request's head branch was updated. For example, the head branch
+    # was updated from the base branch or new commits were pushed to the
+    # head branch.
+    types: [synchronize]
+
+jobs:
+  conflicts:
+    runs-on: ubuntu-latest
+    permissions:
+      pull-requests: write
+    steps:
+      - name: check if PRs are mergeable
+        uses: eps1lon/actions-label-merge-conflict@v2.1.0
+        with:
+          dirtyLabel: "conflicts"
+          repoToken: "${{ secrets.GITHUB_TOKEN }}"
+          commentOnDirty: "This pull request has conflicts, please resolve those so that the changes can be evaluated."
+          commentOnClean: "All conflicts have been resolved, thanks!"
+