Add apache#24599 to CHANGES.md (apache#26020)

Co-authored-by: tvalentyn <tvalentyn@users.noreply.github.com>

CHANGES.md

@@ -72,6 +72,8 @@
   like `df | (Transform1 | Transform2 | ...)` to avoid excessive conversions.)
 * The Go SDK adds new transforms periodic.Impulse and periodic.Sequence that extends support
   for slowly updating side input patterns. ([#23106](https://github.com/apache/beam/issues/23106))
+* Python SDK now requires `protobuf>=4.21.1,<4.23.0` and no longer supports protobuf 3.x. ([#24599](https://github.com/apache/beam/pull/24599))
+* Several Google client libraries in Python SDK dependency chain were updated to latest available major versions. ([#24599](https://github.com/apache/beam/pull/24599))
 
 ## Breaking Changes