Bot errors if repo already has all-contributors branch

[VeckoTheGecko]

UPDATE: See #460 (comment)

Describe the bug
I have tried following all the instructions, but can't get the bot to work on a specific repo (but works on all minimal example repos, and even a fork with main pointing to the same commit using the same call to the bot).

To Reproduce
I've tried, but I can't reproduce this...

Timeline of things I've tried:

• Updated README with below table section (PR) as in docs, and called the bot. Bot gave error message.

Added to README:

## ✨Contributors

Thanks go to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):

<!-- ALL-CONTRIBUTORS-LIST:START - Do not remove or modify this section -->
<!-- prettier-ignore-start -->
<!-- markdownlint-disable -->

<!-- markdownlint-restore -->
<!-- prettier-ignore-end -->

<!-- ALL-CONTRIBUTORS-LIST:END -->

This project follows the [all-contributors](https://allcontributors.org) specification. Contributions of any kind are welcome!

• Bunch of testing to see if I was calling it wrong, or if having no config was the issue (all my bot calls failed).
• Removed the config again for simplicity. Forked the repo and tried, and the fork worked. Both repos had main at the same commit. (original repo bot call, bot call on fork)

Expected behavior
The bot to make a PR instead of replying with "We had trouble processing your request. Please try again later.".

Additional comments
Sorry this is such a weird issue with minimal debugging help from me. Let me know if I can be of any more help, Any ideas?? I'm out of ideas here 😢

[transcental]

Got the same issue on one of my repos: transcental/WhooshServer#2
Been using the bot for a while and never had any issues before.

[VeckoTheGecko]

Realised that this issue stemmed from my repo having an all-contributors branch, which conflicted with the bot as it tries to create branches in the all-contributors/* namespace.

This didn't occur on all forks as the forks may only have been created with the main branch.

Having this issue noted somewhere in docs would be a good addition.

As far as I know, this isn't the same issue faced by @DillonB07