Update core-code-style.md (#19008)

Changed Section 4 from CamelCase to StudlyCase to match the overview and Section 3.

docs/internals/core-code-style.md

@@ -46,7 +46,7 @@ Class names MUST be declared in `StudlyCaps`. For example, `Controller`, `Model`
 
 The term "class" refers to all classes and interfaces here.
 
-- Classes should be named using `CamelCase`.
+- Classes should be named using `StudlyCase`.
 - The brace should always be written on the line underneath the class name.
 - Every class must have a documentation block that conforms to the PHPDoc.
 - All code in a class must be indented with 4 spaces.