Github Actions to Merge upstream branches

merge_upstream_branches.yml

# https://stackoverflow.com/a/61574295/2118504
# .github/workflows/example.yml

name: Merge upstream branches
on:
  schedule:
     # actually, ~5 minutes is the highest
     # effective frequency you will get
    - cron:  '* * * * *'
jobs:
  merge:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
      - name: Merge upstream
        run: |
          git config --global user.name 'your-name'
          git config --global user.email 'your-username@users.noreply.github.com'

          # "git checkout master" is unnecessary, already here by default
          git pull --unshallow  # this option is very important, you would get
                                # complains about unrelated histories without it.
                                # (but actions/checkout@v2 can also be instructed
                                # to fetch all git depth right from the start)

          git remote add upstream https://github.com/example/test.git
          git fetch upstream

          # Neither forget the -b opt,
          # the feature/x ref is ambiguous at this stage
          git checkout -b feature/x origin/feature/x
          git merge --no-edit upstream/feature/x
          git push origin feature/x

          git checkout master
          git merge --no-edit upstream/master
          git push origin master

          # etc