Update changelogs from fern repo (#891)

Co-authored-by: Swimburger <[email protected]>

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2025-09-05.mdx

@@ -1,5 +1,5 @@
 ## 2.1.16-rc0
 **`(fix):`** Enable type disambiguation and renaming during code generation
-Permits the `examples` test fixtures to compile sucessfully
+Permits the `examples` test fixtures to compile successfully
 
 

fern/products/sdks/overview/python/changelog/2025-06-20.mdx

@@ -1,7 +1,7 @@
 ## 4.22.1-rc0
 **`(feat):`** Lazily validate model serialization to reduce memory consumption. Pydantic 2.11.0 introduced an issue where the model_serializer 
 decorator set to wrap mode forced it to eagerly do schema validation at import time. Because we had this decorator on the UniversalBaseModel,
-it would try to validate the schemas of all the Model types at import time. This caused massive memory spikes for more complex SDKs, upto 2.6GB
+it would try to validate the schemas of all the Model types at import time. This caused massive memory spikes for more complex SDKs, up to 2.6GB
 in some cases. This change essentially accomplishes the same logic of wrapping the serialization process and modifying the serialization
 structure of datetime fields. The difference is that we manually wrap, so we're able to defer model validation until runtime, drastically
 reducing our memory consumption.