benchmark-data-repository exists and isn't empty

We have two separate workflows, whom both use this action and I think they're interfering with each other when they both want to post their results as comment.

See error message:
```
/usr/bin/git -c user.name=github-action-benchmark -c user.email=github@users.noreply.github.com -c http.https://github.com/.extraheader= clone ***github.com/Ultimaker/CuraEngineBenchmarks.git ./benchmark-data-repository
fatal: destination path './benchmark-data-repository' already exists and is not an empty directory.
Error: Command 'git' failed with args '-c user.name=github-action-benchmark -c user.email=github@users.noreply.github.com -c http.https://github.com/.extraheader= clone ***github.com/Ultimaker/CuraEngineBenchmarks.git ./benchmark-data-repository': fatal: destination path './benchmark-data-repository' already exists and is not an empty directory.
: Error: The process '/usr/bin/git' failed with exit code 128
```
https://github.com/Ultimaker/CuraEngine/actions/runs/5835175234/job/15826271497#step:19:110

Workflows:
- Google Benchmarks: https://github.com/Ultimaker/CuraEngine/blob/33790412b61f33e4f4bfe1af2512f2f621e7aff5/.github/workflows/benchmark.yml#L153
- customBiggerIsBetter: https://github.com/Ultimaker/CuraEngine/blob/33790412b61f33e4f4bfe1af2512f2f621e7aff5/.github/workflows/gcodeanalyzer.yml#L295