Update changelogs from fern repo (#4488)

Co-authored-by: iamnamananand996 <31537362+iamnamananand996@users.noreply.github.com>

Author: fern-support

fern/products/sdks/overview/rust/changelog/2026-03-22.mdx

@@ -1,3 +1,11 @@
+## 0.26.1
+**`(fix):`** Fix convenience constructors for union variants whose optional fields have nested
+optional/nullable IR wrappers (e.g. `optional<nullable<string>>` from OpenAPI).
+Previously only one layer was unwrapped, leaving the parameter as `Option<T>` instead
+of `T`, which caused `E0308 mismatched types` compilation errors. Now all
+optional/nullable layers are stripped to produce the correct bare type.
+
+
 ## 0.26.0
 **`(feat):`** Generate convenience constructors for discriminated union variants with optional fields.
 For each optional field in an inlined variant, a `{variant}_with_{field}` constructor is