Update changelogs from fern repo (#4259)

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-03-13.mdx

@@ -1,3 +1,11 @@
+## 2.28.0
+**`(feat):`** Generate a separate WireMock server for each test fixture instead of sharing
+a single global server across all mock server tests. Each test class now starts
+and stops its own `WireMockServer` in `[OneTimeSetUp]`/`[OneTimeTearDown]`,
+and test fixtures are annotated with `[Parallelizable(ParallelScope.Self)]`
+so NUnit can run them in parallel.
+
+
 ## 2.27.1
 **`(fix):`** Fix retry test assertions to match the SDK's indented JSON serialization.