include: Renamed begin_code.h and close_code.h to have SDL_ prefixes.

Fixes #6864.

include/SDL3/SDL_test_harness.h

@@ -36,7 +36,7 @@
 #ifndef SDL_test_h_arness_h
 #define SDL_test_h_arness_h
 
-#include <SDL3/begin_code.h>
+#include <SDL3/SDL_begin_code.h>
 /* Set up for C function definitions, even when using C++ */
 #ifdef __cplusplus
 extern "C" {
@@ -127,7 +127,7 @@ int SDLTest_RunSuites(SDLTest_TestSuiteReference *testSuites[], const char *user
 #ifdef __cplusplus
 }
 #endif
-#include <SDL3/close_code.h>
+#include <SDL3/SDL_close_code.h>
 
 #endif /* SDL_test_h_arness_h */