Update ui test suite to nightly-2025-09-12

Author: dtolnay

tests/ui/expression-fallback.stderr

@@ -11,6 +11,11 @@ error: argument never used
  | -- ^^^^^^ argument never used
  | |
  | formatting specifier missing
+ |
+help: format specifiers use curly braces, consider adding a format specifier
+ |
+4 | #[error("{}".yellow)]
+ | ++
 
 error[E0425]: cannot find value `yellow` in this scope
  --> tests/ui/expression-fallback.rs:4:12