Version 1.21.0

This version adds some small bug fixes and improvements to certain checks.

What's Changed

• Add example config files by @dosisod in #280
• Fix tests failing in Python 3.12 by @dosisod in #281
• Detect not when used with startswith and endswith by @dosisod in #282
• Only allow built-in mapping types in FURB173 by @dosisod in #284
• Improve FURB111, bump version by @dosisod in #285

Full Changelog: v1.20.0...v1.21.0