Update changelogs from fern repo (#3343)

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

Author: fern-support

fern/products/sdks/overview/csharp/changelog/2026-01-28.mdx

@@ -1,3 +1,17 @@
+## 2.19.5
+**`(fix):`** Fix missing client-level headers for endpoints without endpoint-specific headers.
+
+Previously, endpoints that didn't have endpoint-specific headers (like custom request headers)
+would not include client-level headers (API key, SDK version, additional headers) in their
+HTTP requests. This caused authentication failures for APIs that rely on headers set at the
+client level.
+
+The fix ensures that all endpoints now properly merge headers from:
+* Client options headers (API key, SDK version, etc.)
+* Client additional headers (user-provided at client construction)
+* Request options additional headers (user-provided per-request)
+
+
 ## 2.19.4
 **`(fix):`** Fix missing `[Optional]` and/or `Nullable` attributes on generated properties with defaults.