Inline format! args wherever possible

tests/no_duplicate_extensions.rs

@@ -30,8 +30,7 @@ fn no_duplicate_extensions() {
         for extension in &syntax.file_extensions {
             assert!(
                 KNOWN_EXCEPTIONS.contains(&extension.as_str()) || extensions.insert(extension),
-                "File extension / pattern \"{}\" appears twice in the syntax set",
-                extension
+                "File extension / pattern \"{extension}\" appears twice in the syntax set"
             );
         }
     }