A github action fails a workflow if the branch is not up to date with the target branch. You must add a branch protection rule of Require branches to be up to date before merging.

Add to your workflow the following contents:

name: workflow

on:
  push:
    branches: [ '**' ]
  pull_request:
    branches: [ '**' ]

jobs:
  full_ci:
    runs-on: ubuntu-18.04

    steps:
      - uses: guyarb/[email protected]

1. Fork this repo.
2. Create a branch with your feature/bugfix.
3. Open a PR to me.

Please open issues for any bug or suggestion you have.