chore: release note for #18495 (#18499)

# Overview

Adds #18495 to the release notes for the 8.4.1 hotfix.

## Changelog

+1 line

## Review requests

This should only merge after the fix does, naturally.

## Risk assessment

zip

Author: ecormany

app-shell/build/release-notes.md

@@ -14,6 +14,7 @@ The 8.4.1 hotfix release fixes two issues:
 
 - Placing a Magnetic Block in slot C2 no longer prevents Labware Position Check from running.
 - Existing labware offsets are no longer doubled during Labware Position Check.
+- The app no longer crashes during run setup when using certain custom labware.
 
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