sdl2-compat: Use the sdl2-compat namespace for properties used internally

SDL Commits
1 
From c64c7ad3c551c45fe910f8e5b9438b3a54ac9d86 Mon Sep 17 00:00:00 2001
From: Sam Lantinga <[EMAIL REDACTED]>
Date: Thu, 9 Nov 2023 10:42:15 -0800
Subject: [PATCH] Use the sdl2-compat namespace for properties used internally

---
 src/sdl2_compat.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/sdl2_compat.c b/src/sdl2_compat.c
index 9c45b01..18c619c 100644
--- a/src/sdl2_compat.c
+++ b/src/sdl2_compat.c
@@ -5336,7 +5336,7 @@ SDL_GetWindowFlags(SDL_Window *window)
     return flags;
 }
 
-#define POPUP_PARENT_PROP_STR "SDL.internal.parentWnd"
+#define POPUP_PARENT_PROP_STR "sdl2-compat.window.parent"
 
 DECLSPEC void* SDLCALL
 SDL_GetWindowData(SDL_Window * window, const char *name)