xdg-shell: viewport size change not accepted as size change (wants new buffer)
In response to a configure event, a Wayland client may choose to set a viewport size or destination to make a surface fit the requested size, without attaching a new buffer. This is currently prevented by https://gitlab.gnome.org/GNOME/mutter/-/blob/1f1bf4cd9d1c8a18c7ae1dd7f5e69be32546fa7c/src/wayland/meta-wayland-xdg-shell.c#L813-814
Similar to #1716 (closed) and fixed by !1795 (b54b6efe). Still filing this one in case !1795 (merged) needs changes.