Need to update bottle for py3.13

[dgw]

Python 3.13 removed cgi from the standard library, which bottle 0.12 uses for multipart form data parsing. bottle 0.13 switched to bundling a parser "borrowed from multipart", so it continues to work on Python 3.13.

This plugin already dropped support for Python <3.8 and requires Sopel 8.0+, so bottle 0.13 dropping the older Python versions won't be a problem. We should "just" have to soak-test the new dependency version in prod for a bit.