title: Git Push Error "cannot lock ref" "reference already exists"
body: <p>The full error is: </p>
  
  <p>remote: error: cannot lock ref 'refs/heads/fix/add_overlay': reference already exists  </p>
  
  <p>I'm using SourceTree, but that should not matter I don't think. I keep trying to push and I keep getting this error, how can I resolve it?  </p>