chore: fix markdown error breaking publish workflow (#948)

Author: devalog

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

@@ -7,7 +7,7 @@
 
 
 ## 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.