fix(typo): fixed typo in cpp namespaces (#4122)

src/data/roadmaps/cpp/content/106-structuring-codebase/100-scope/100-namespaces.md

@@ -57,7 +57,7 @@ int main() {
 }
 ```
 
-##`using` Keyword
+## `using` Keyword
 
 You can use the `using` keyword to import namespaced elements into the current scope. However, this might lead to name conflicts if multiple namespaces have elements with the same name.