InstallGStreamerResources returns wrong result

gnome-software-40.0-2.fc34.x86_64 PackageKit-1.2.3-1.fc34.x86_64

Reproducer:

start a normal session
if necessary, install gstreamer1-plugin-openh264 and restart the session
make sure that gnome-software is started in the background
run sudo rpm -e gstreamer1-plugin-openh264-1.18.2-1.fc34.x86_64
launch totem foo.mp4
gnome-software will start, show a list of possible packages to install
clicking on the Install button for the openh264 package will fail

An instrumented version of the PackageKit client shows that gnome-software returns no errors, so that totem will start playing (in the background, but that's another matter) as if the new codec was successfully installed.