chore: release note for floating point distribute bug fix (#19033)

# Overview

Add a line for
[AUTH-2151](https://opentrons.atlassian.net/browse/AUTH-2151) in the
8.5.1 release notes.

## Test Plan and Hands on Testing

n/a

## Changelog

- 1 new bullet
- Simplified note for air gap bug per [post-merge discussion on
#19017](#19017 (comment))

## Review requests

good words?

## Risk assessment

none

[AUTH-2151]:
https://opentrons.atlassian.net/browse/AUTH-2151?atlOrigin=eyJpIjoiNWRkNTljNzYxNjVmNDY3MDlhMDU5Y2ZhYzA5YTRkZjUiLCJwIjoiZ2l0aHViLWNvbS1KU1cifQ

Author: ecormany

api/release-notes.md

@@ -14,7 +14,8 @@ The 8.5.1 hotfix release fixes these bugs:
 
 - Corrected behavior when performing multi-dispense actions using a custom or modified liquid class.
 - Fixed a problem where certain quick transfers (specifically ones that attempt to blow out over the waste chute) could not be run.
-- Air-gapping after a dispense when using a liquid class now uses the correct volume. It previously used the same volume as when air-gapping after an aspirate.
+- Air-gapping after a dispense when using a liquid class now uses the correct volume.
+- Fixed a problem where distributing with a liquid class would sometimes fail to blow out the disposal volume.
 
 ---