Set editor hint early for Project Manager and Editor

We need it in setup() already before initializing the renderer,
as it's used to force fallback to GLES2 if GLES3 fails.

Fixes #26806.

main/main.cpp

@@ -856,6 +856,7 @@ Error Main::setup(const char *execpath, int argc, char *argv[], bool p_second_ph
 	}
 
 	if (editor || project_manager) {
+		Engine::get_singleton()->set_editor_hint(true);
 		use_custom_res = false;
 		input_map->load_default(); //keys for editor
 	} else {