Goal

So, you are hoping:

automatically reformat code pushed to PR?
automatically merge one branch into another at a certain cadence?
something else involving automatically creating and pushing git commits?

All of these can be solved using a GitHub Action workflow!

There are different ways to set up your workflow, with varying levels of control over the result. This article describes the most dead-simple way I could come up with.

My solution

First, make sure GitHub Actions are enabled for your repository. Make sure that GitHub Actions has write access to your repository – this can be done in repo settings.

Now, add a workflow named <your-workflow-name>.yml to ./.github/workflows/, following this template:

name: Name of your workflow

on:
  push:
    branches: [ ... ]  # Replace ... with the branches you want to trigger upon.

jobs:
  job-name:  # set your job name to something nice.
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v2
        with:
          fetch-depth: 0  # all branches and tags
      - name: Set git identity
        run: |
          git config user.name 'github-actions[bot]'
          git config user.email 'github-actions[bot]@users.noreply.github.com'
      # ...
      # ADD YOUR GIT OPERATION STEPS HERE
      # ...
      - name: Push
        run: |
          git remote set-url origin https://x-access-token:${{ github.token }}@github.com/${{ github.repository }}
          git push

Example: tutor-contrib-coursegraph/.github/workflows/merge-to-nightly.yml at master · openedx/tutor-contrib-coursegraph

Discussion

Pros

This approach is very simple to set up.
Using github-actions[bot] gives you the GitHub logo as the profile picture on the commit.
github-actions[bot] isn’t a real GitHub user account, which will hopefully make it clear that a user account isn’t responsible for commits that the action makes.

Cons:

For the branches being pushed to, you cannot have protections that require a PR or any status checks. This is probably a showstopper if you’re hoping to push to master or any other critical branch.

Improvements

If you want to push to a branch without making the branch unprotected, you may want to ditch the github.token strategy for in favor of authenticating as a GitHub App. This would allow you to protect the target branch, while marking the GitHub App as an explicit exception to the branch protection.