Comment 0 for bug 1874469

[Impact]

Every so often update-manager can hang during snap updates. When this occurs the application must be force closed.

[Test Case]

Repeating the following will eventually cause a hang on "Installing snap-store snap".

`
sudo apt -y install gnome-software
sudo apt-mark auto gnome-software

snap remove snap-store
rm -rf ~/snap/snap-store

update-manager
`

[Regression Potential]

The fix is trivial (see linked branch), in fact, GLib.idle_add() was applied correctly elsewhere, it was just missed here.