Update changelogs from fern repo (#5305)

Co-authored-by: dsinghvi <10870189+dsinghvi@users.noreply.github.com>

Author: fern-support

fern/products/sdks/generators/csharp/changelog/2026-05-01.mdx

@@ -0,0 +1,18 @@
+## 2.64.2
+**`(fix):`** Dedup auth-derived headers in the generated client constructor when
+multiple auth schemes resolve to the same HTTP header name (for
+example, an oauth2 bearer scheme plus an apiKey-in-header scheme
+both named `Authorization`). Previously the constructor's
+`Dictionary<string, string>` collection initializer added the same
+key twice and threw `System.ArgumentException: An item with the
+same key has already been added` at runtime. Earlier auth schemes
+win, preserving the ordering established by the IR.
+
+
+**`(fix):`** Fix literal boolean auth-header values being emitted as `"True"` regardless
+of the configured value. The generated client constructor's auth-header
+dictionary tested the truthiness of the `Literal` discriminated-union
+object instead of reading its `boolean` field, so a literal `false` header
+incorrectly produced `"True"`.
+
+