I find this bot annoying, especially since it seems to require matching manual updates to requirements.txt.

Oh, I actually quite like it. I agree that dependabot wouldn't be useful for typeshed, given that upgrading mypy/pyright often requires a lot of changes to typeshed. But the pre-commit bot generally only suggests changes that are pretty easy to merge (though, yes, we need to make changes to requirements-tests.txt), and it's pretty easy to forget to update dependencies otherwise.

Can we make it do this like once every six months?

I wouldn't object to that! According to the docs, the options are weekly, monthly or quarterly: https://pre-commit.ci/#configuration-autoupdate_schedule

The stubtest failure is because of the release of 3.10.6 a few days ago.