Remove pulling specific branch since this will only run on the default branch

Author: Nate Wiebe

.github/workflows/auto-update.yml

@@ -17,7 +17,6 @@ jobs:
                 uses: actions/checkout@v2
                 with:
                     ssh-key: ${{ secrets.SSH_PRIVATE_KEY }}
-                    ref: 'v2.0'
 
             -   name: Setup PHP
                 uses: shivammathur/setup-php@v2