Many Superfluous Timestamped Files?

Thank you for creating nbgitpuller which I have used successfully in a number of different JupyterHubs I administer.

### Bug description

In some cases, I have noticed that it is producing many timestamped files that do not seem to meet the “case 5” criteria. The timestamped files have a regular repository file analog (e.g., LICENSE vs. LICENSE__20201023185900 where LICENSE is a regular repo file that has been present all along and has not changed). Moreover, when doing a diff between the timestamped file and the regular repo file, there are no differences, they are exactly identical. What is the reason for all these superfluous timestamped files? From what I have seen, it does this for almost every file in the repo. Has anyone else noticed this problem?

#### Expected behavior

No superfluous timestamped files.

#### Actual behavior

Many superfluous timestamped files.

### How to reproduce

I have tried to reproduce this problem with dummy repos, but I have not been successful so far. I will keep trying though. I have observed this problem across multiple repositories. I am hoping that someone else has seen this behavior.

### Your personal set up

- OS: Ubuntu 20.04

- Version: JupyterHub 1.1.0 20200813173441