cronjob auto-PR: try to fix setting the remote branch

src/tools/miri/.github/workflows/ci.yml

@@ -11,7 +11,7 @@ on:
       - 'master'
   schedule:
     - cron: '6 6 * * *' # At 6:06 UTC every day.
-    - cron: '42 * * * *' # Also each hour, for testing
+    - cron: '12 * * * *' # Also each hour, for testing
 
 env:
   CARGO_UNSTABLE_SPARSE_REGISTRY: 'true'
@@ -203,9 +203,7 @@ jobs:
           ./miri toolchain
           ./miri fmt --check || (./miri fmt && git commit -am "fmt")
       - name: Push changes to a branch
-        run: |
-          git switch -c "rustup$(date -u +%Y-%m-%d)"
-          git push -u
+        run: git push -u origin HEAD:"rustup$(date -u +%Y-%m-%d)"
       - name: Create Pull Request
         run: gh pr create -B master --title 'Automatic sync from rustc' --body ''
         env: