Use literal blocks for code samples with GDScript.

GDScript is already the default, it's redundant to specify it explicitly.
A [literal block][1] is already enough.

  [1]: https://www.sphinx-doc.org/en/1.8/usage/restructuredtext/basics.html#rst-literal-blocks

tutorials/plugins/android/android_plugin.rst

@@ -264,7 +264,7 @@ The module should include the full Java path. For our example: ``org/godotengine
 
 Then, from your script:
 
-.. code::
+::
 
     if Engine.has_singleton("MySingleton"):
         var singleton = Engine.get_singleton("MySingleton")