Add a merge conflict check. (#8626)

* Add a merge conflict check.

This is directly copied from https://github.com/wixoaGit/OpenDream/pull/648

* Update .github/workflows/conflict-labeler.yml

Co-authored-by: ike709 <ike709@users.noreply.github.com>

Co-authored-by: ike709 <ike709@users.noreply.github.com>

.github/workflows/conflict-labeler.yml

@@ -0,0 +1,18 @@
+name: Check Merge Conflicts
+
+on:
+  push:
+    branches:
+      - master
+  pull_request_target:
+
+jobs:
+  Label:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Check for Merge Conflicts
+        uses: eps1lon/actions-label-merge-conflict@513a24fc7dca40990863be2935e059e650728400
+        with:
+          dirtyLabel: "Merge Conflict"
+          repoToken: "${{ secrets.GITHUB_TOKEN }}"
+          commentOnDirty: "This pull request has conflicts, please resolve those before we can evaluate the pull request."