deps(amazonq): update mynah ui to 4.21.3 (#6276)

## Problem
- mynah ui 4.21.3 contains a fix needed for tests:
https://github.com/aws/mynah-ui/releases/tag/v4.21.3

## Solution
- update to it. No public facing changes are needed

Author: jpinkney-aws

package-lock.json

@@ -508,7 +508,7 @@
         "@aws-sdk/property-provider": "3.46.0",
         "@aws-sdk/smithy-client": "^3.46.0",
         "@aws-sdk/util-arn-parser": "^3.46.0",
-        "@aws/mynah-ui": "^4.21.2",
+        "@aws/mynah-ui": "^4.21.3",
         "@gerhobbelt/gitignore-parser": "^0.2.0-9",
         "@iarna/toml": "^2.2.5",
         "@smithy/middleware-retry": "^2.3.1",