fix depth_prepass_alpha not work in compatibility mode

drivers/gles3/rasterizer_scene_gles3.cpp

@@ -1420,7 +1420,7 @@ void RasterizerSceneGLES3::_fill_render_list(RenderListType p_render_list, const
 #else
 				bool force_alpha = false;
 #endif
-				if (!force_alpha && (surf->flags & GeometryInstanceSurface::FLAG_PASS_OPAQUE)) {
+				if (!force_alpha && (surf->flags & (GeometryInstanceSurface::FLAG_PASS_DEPTH | GeometryInstanceSurface::FLAG_PASS_OPAQUE))) {
 					rl->add_element(surf);
 				}
 				if (force_alpha || (surf->flags & GeometryInstanceSurface::FLAG_PASS_ALPHA)) {