video: Default SDL_GL_FRAMEBUFFER_SRGB_CAPABLE back to zero.

(This was corrected in main, but there isn't a clean cherry-pick we can do for
the release-3.4.x branch at this point, since various pieces of the sRGB work
made it in here in a different order, but this is the one crucial line that
appears to be missing.)

Reference Issue #14898.

src/video/SDL_video.c

@@ -4991,7 +4991,7 @@ void SDL_GL_ResetAttributes(void)
     }
 
     _this->gl_config.flags = 0;
-    _this->gl_config.framebuffer_srgb_capable = -1;
+    _this->gl_config.framebuffer_srgb_capable = 0;
     _this->gl_config.no_error = 0;
     _this->gl_config.release_behavior = SDL_GL_CONTEXT_RELEASE_BEHAVIOR_FLUSH;
     _this->gl_config.reset_notification = SDL_GL_CONTEXT_RESET_NO_NOTIFICATION;