chore: add Grit updates to CHANGELOG (#3989)

CHANGELOG.md

@@ -69,6 +69,21 @@ our [guidelines for writing a good changelog entry](https://github.com/biomejs/b
 
 - The CSS parser now accepts the characters U+FFDCF and U+FFFD in identifiers. Contributed by @Conaclos
 
+### GritQL
+
+#### New features
+
+- Added support for custom definitions, including:
+  - Pattern and predicate definitions: https://docs.grit.io/guides/patterns
+  - Function definitions: https://docs.grit.io/language/functions#function-definitions
+
+  Contributed by @arendjr
+
+#### Bug fixes
+
+- Fixed an issue that caused `contains` queries to report false positives when the matched node
+  appeared inside a sibling node. Contributed by @arendjr
+
 ## v1.9.1 (2024-09-15)
 
 ### CLI