[Complex Test Layouts] Change String to use UTF-32 encoding on all platforms.

tests/SCsub

@@ -6,6 +6,9 @@ env.tests_sources = []
 
 env_tests = env.Clone()
 
+# Include GDNative headers.
+env_tests.Append(CPPPATH=["#modules/gdnative/include"])
+
 # We must disable the THREAD_LOCAL entirely in doctest to prevent crashes on debugging
 # Since we link with /MT thread_local is always expired when the header is used
 # So the debugger crashes the engine and it causes weird errors