Add a changelog for retries update (#4791)

* Add a changelog for retries update

Author: ubaskota

.changes/1.43.3.json

@@ -38,5 +38,10 @@
     "category": "``vpc-lattice``",
     "description": "[``botocore``] Amazon VPC Lattice now supports privately resolvable DNS resources",
     "type": "api-change"
+  },
+  {
+    "category": "``Retries``",
+    "description": "[``botocore``] Added opt-in support for updated standard retry behavior via the `AWS_NEW_RETRIES_2026` environment variable. This environment variable is temporary and will be removed in a future release when the updated behavior becomes the default. Changes include updated default retry mode to ``standard``, service-specific max attempts for DynamoDB, revised retry quota costs based on error type, updated exponential backoff with service-specific scale factors, ``x-amz-retry-after`` header support, and long-polling operation backoff on quota exhaustion.",
+    "type": "enhancement"
   }
-]
+]