replace bors with mergify

.github/workflows/test.yml

@@ -4,8 +4,6 @@ on:
   push:
     branches:
       - master
-      - staging
-      - release-*
   schedule:
     - cron:  '51 2 * * *'
 jobs:

.github/workflows/upgrade-flakes.yml

@@ -18,9 +18,5 @@ jobs:
         uses: DeterminateSystems/update-flake-lock@v19
         with:
           token: ${{ secrets.GH_TOKEN_FOR_UPDATES }}
-          pr-body: |
-            Automated changes by the update-flake-lock
-            ```
-            {{ env.GIT_COMMIT_MESSAGE }}
-            ```
-            bors merge
+          pr-labels: |
+            merge-queue