Update changelogs from fern repo (#4505)

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 @@
+## 2.53.0
+**`(fix):`** Enforce `global::` prefix on all `System` namespace references in generated code.
+This prevents CS0118/CS0426 compile errors when customer projects define a type or
+namespace named `System` (e.g., root namespace `Foo.Net` with a class `System`).
+All `using System.*` directives and inline `System.*` type references now use
+`global::System.*`. A CI validation script in seed.yml enforces this going forward.
+
+
 ## 2.52.0
 **`(feat):`** Conditionally emit System.Text.Json as a PackageReference only when
 targeting pre-net8.0 TFMs (netstandard2.0, net462). The package is