non-fast-forward error when auto-push is disabled

I am trying to configure my benchmarking so that benchmarks are only saved on pushes to the main branch. I still want the benchmarking to be run on PRs so that I can recieve alerts about performance degradations before merging.

When `auto-push` is disabled in [my benchmarking config](https://github.com/eyereasoner/eye-js/blob/ef0fed97097db32a7c8f38dc15ec2bbf935c27e2/.github/workflows/nodejs.yml#L51-L90) I get [this workflow error](https://github.com/eyereasoner/eye-js/actions/runs/4906541384/jobs/8761075845?pr=299); even though I am expecting nothing to be pushed.

With `save-data-file` disabled and `auto-push` enabled on branches that are not main (tested [here](https://github.com/eyereasoner/eye-js/pull/299/commits/b9e4eed4c3047db9cda5a61661e5d38b97d66886)); I am still seeing data get pushed to by [bench-pages](https://github.com/eyereasoner/eye-js/tree/bench-pages) branch.

I raised the same issue [here](https://github.com/benchmark-action/github-action-benchmark/issues/173) yesterday and closed it thinking there was a race condition. It is not, I had just changed the `auto-push` parameter.

Possibly related to #158