Update changelogs from fern repo (#4423)

Co-authored-by: Swimburger <3382717+Swimburger@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-03-20.mdx

@@ -1,3 +1,11 @@
+## 2.45.0
+**`(feat):`** Add `InjectTestMessage` internal method to generated WebSocket client classes.
+This allows unit tests to simulate incoming WebSocket messages by injecting raw
+JSON strings through the normal `OnTextMessage` pipeline without requiring a real
+WebSocket connection. The method is marked `internal` so it is only accessible
+via `[InternalsVisibleTo]` in test projects, keeping the public API surface clean.
+
+
 ## 2.44.0
 **`(feat):`** Add queued sending via `Channel<T>` to the WebSocket connection layer. Two
 unbounded channels (text and binary) are drained by dedicated background tasks