Update changelogs from fern repo (#925)

Co-authored-by: patrickthornton <[email protected]>

Author: fern-support

fern/products/cli-api-reference/cli-changelog/2025-09-22.mdx

@@ -1,9 +1,13 @@
+## 0.78.6
+**`(fix):`** Support `null` in an `enum` (functionality is delegated to `nullable<>`).
+
+
 ## 0.78.5
 **`(fix):`** Correct `nullable<>` wrapping of nullable schemas referenced via `$ref`.
 
 
 ## 0.78.4
-**`(fix):`** Collapse any combination of optional and nullable to `optional<nullable<T>>`.
+**`(fix):`** Collapse any combination of optional and nullable to optional<nullable<T>>.
 
 ## 0.78.3
 **`(chore):`** Support IR v59 in the Rust SDK generator.