chore: Adds note about numerical x-axis (#26208)

Co-authored-by: John Bodley <4567245+john-bodley@users.noreply.github.com>
(cherry picked from commit b4a35e6)

UPDATING.md

@@ -24,6 +24,7 @@ assists people when migrating to a new version.
 
 ## 3.1.0
 
+- [26034](https://github.com/apache/superset/issues/26034): Fixes a problem where numeric x-axes were being treated as categorical values. As a consequence of that, the way labels are displayed might change given that ECharts has a different treatment for numerical and categorical values. To revert to the old behavior, users need to manually convert numerical columns to text so that they are treated as categories. Check https://github.com/apache/superset/issues/26159 for more details.
 - [24657](https://github.com/apache/superset/pull/24657): Bumps the cryptography package to augment the OpenSSL security vulnerability.
 
 ### Other