Update merge-to-main script (#1420)

* Before creating the merge-main PR, branch it off main, so merge conflicts can be addressed in the branch rather than by committing to main. * Format.

Author: jonsimantov

.github/workflows/update-feature-branches.yml

@@ -17,6 +17,8 @@ env:
  defaultBranchPattern: "feature_branch/*"
  defaultMainBranch: "main"
  triggerTestsLabel: "tests-requested: quick"
+ branchPrefix: "workflow/auto-merge-feature-branch-"
+
 
 jobs:
  list_feature_branches:
@@ -85,6 +87,11 @@ jobs:
  python scripts/gha/install_prereqs_desktop.py
  python -m pip install requests
 
+ - name: Name new branch
+ run: |
+ date_str=$(date "+%Y%m%d-%H%M%S")
+ echo "NEW_BRANCH=${{env.branchPrefix}}${{github.run_number}}-${date_str}" >> $GITHUB_ENV
+
  - name: Create merge PR
  id: create-pr
  run: |
@@ -115,7 +122,10 @@ jobs:
 
  > Created on ${date_str} by [${{github.workflow}} workflow]($GITHUB_SERVER_URL/$GITHUB_REPOSITORY/actions/runs/$GITHUB_RUN_ID).
  "
- pr_number=$(python scripts/gha/create_pull_request.py --token ${{ steps.generate-token.outputs.token }} --base "${{ matrix.branch_name }}" --head "${main_branch}" --title "${pr_title}" --body "${pr_body}")
+ git checkout main
+ git checkout -b "${NEW_BRANCH}"
+ git push --set-upstream origin "${NEW_BRANCH}"
+ pr_number=$(python scripts/gha/create_pull_request.py --token ${{ steps.generate-token.outputs.token }} --base "${{ matrix.branch_name }}" --head "${NEW_BRANCH}" --title "${pr_title}" --body "${pr_body}")
  echo "created_pr_number=${pr_number}" >> $GITHUB_OUTPUT
 
  - name: Set test trigger label.