fix calculation of temp_dir in delete_if_cache_directory()

[0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q]

close #1125

[github-actions[bot]]

This is how benchmark results would change (along with a 95% confidence interval in relative change) if aeaa1faef2e5ea11be26817d8cfa3774ad9d66e7 is merged into main:

Further explanation regarding interpretation and methodology can be found in the documentation.

[lorenzwalthert]

Thanks!