docs: fix heading level of Manual > Modules > init & precomp (#43996)

Author: tfiers

doc/src/manual/modules.md

@@ -394,7 +394,7 @@ end
 end
 ```
 
-### Module initialization and precompilation
+## Module initialization and precompilation
 
 Large modules can take several seconds to load because executing all of the statements in a module
 often involves compiling a large amount of code.