auto incremented wrong tag

We're trying to set up a repository providing a Python library for working with a certain data schema. The library version and the schema version are separate, and so we decided to tag releases with two sets of tags: tags of the form `x.y.z` are for library releases, while tags of the form `schema-a.b.c` are for the first release that implements the given schema version. Unfortunately, for some reason, when we tried releasing with `auto` moments ago, it picked up the `schema-*` tags as the tags to increment, leading to all sorts of issues. [Here are the GitHub Actions logs](https://github.com/dandi/dandischema/runs/2696992913?check_suite_focus=true); you may have to scroll up to see all of the diagnostic output from `auto shipit -vv`.

EDIT: On further investigation, it looks like `auto` didn't actually *increment* the `schema-*` tag; it just saw the pre-existing tag and used that for the release.