Fix small typo in the GDExtension C++ example (#7224)

* Fix typo in the GDExtension C++ example

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Co-authored-by: Yuri Sizov <[email protected]>

tutorials/scripting/gdextension/gdextension_cpp_example.rst

@@ -412,7 +412,7 @@ GDScript allows you to add properties to your script using the ``export``
 keyword. In GDExtension you have to register the properties with a getter and
 setter function or directly implement the ``_get_property_list``, ``_get`` and
 ``_set`` methods of an object (but that goes far beyond the scope of this
-tutorial.
+tutorial).
 
 Lets add a property that allows us to control the amplitude of our wave.