sdl2-compat: Use the internal SDL property namespace for parent window tracking

SDL Commits
1 
From 7a7233e17ae417e62858e9d00cfea3553eb2ef6f Mon Sep 17 00:00:00 2001
From: Frank Praznik <[EMAIL REDACTED]>
Date: Thu, 9 Nov 2023 12:29:48 -0500
Subject: [PATCH] Use the internal SDL property namespace for parent window
 tracking

---
 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 572229d..9c45b01 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 "__SDL3_parentWnd"
+#define POPUP_PARENT_PROP_STR "SDL.internal.parentWnd"
 
 DECLSPEC void* SDLCALL
 SDL_GetWindowData(SDL_Window * window, const char *name)