ci: remove merge conflict notifier job.

Seems to be broken and it's not worth debugging.

.github/workflows/test.yaml

@@ -10,16 +10,6 @@ on:
     - master
 
 jobs:
-  # https://github.com/Marr11317/ConflictAdviser
-  notify-merge-conflicts:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: Marr11317/ConflictAdviser@v1
-        with:
-          github_token: ${{ secrets.GITHUB_TOKEN }}
-          conflict_label: "merge conflict"
-          comment: 'Rebase needed'
-
   test:
     runs-on: ubuntu-latest
     container: ubuntu:20.04