Release tarball has missing `gnome-pwa-list` subproject

Both
https://download.gnome.org/sources/gnome-software/47/gnome-software-47.3.tar.xz
and
https://download.gnome.org/sources/gnome-software/48/gnome-software-48.alpha2.tar.xz
build ends with:

meson.build:246:18: ERROR: Subproject exists but has no meson.build file.

It's due to the subprojects/gnome-pwa-list/, which the tarball has, but it's empty. The previous versions have it included with the actual project files.