GPU: Bump MAX_COLOR_TARGET_BINDINGS to 8 (#13937)

src/gpu/SDL_sysgpu.h

@@ -35,7 +35,7 @@
 #define UNIFORM_BUFFER_SIZE            32768
 #define MAX_VERTEX_BUFFERS             16
 #define MAX_VERTEX_ATTRIBUTES          16
-#define MAX_COLOR_TARGET_BINDINGS      4
+#define MAX_COLOR_TARGET_BINDINGS      8
 #define MAX_PRESENT_COUNT              16
 #define MAX_FRAMES_IN_FLIGHT           3