Fix formatting in docs

crates/ruff_linter/src/rules/ruff/rules/mutable_fromkeys_value.rs

@@ -21,7 +21,7 @@ use crate::checkers::ast::Checker;
 ///
 /// ## Example
 /// ```python
-/// cities = dict.fromkeys(["UK", "Poland"],[])
+/// cities = dict.fromkeys(["UK", "Poland"], [])
 /// cities["UK"].append("London")
 /// cities["Poland"].append("Poznan")
 /// print(cities)  # {'UK': ['London', 'Poznan'], 'Poland': ['London', 'Poznan']}