Rollup merge of rust-lang#91035 - GuillaumeGomez:put-back-removed-empty-line, r=camelid

Put back removed empty line

Fixes comment from rust-lang#90438 (comment).

r? ```@camelid```

Author: matthiaskrgr

src/doc/rustdoc/src/unstable-features.md

@@ -398,6 +398,7 @@ undocumented item:
 ```rust
 /// This item has documentation
 pub fn foo() {}
+
 pub fn no_documentation() {}
 ```