Comment 0 for bug 1891599

An exception is randomly happening while ubiquity calling cachedpkg.mark_install() [1].
cachedpkg.mark_install() came from Cache class of python3-apt package.

It looks a timing issue while ubiquity calling cachedpkg.mark_install(), and a retry can workaround it.

The reproduce rate is be about 1/15.

Looks there're 2 things can be improved.
1. improve the fault tolerance of Ubiquity while it calling external library.
2. impvove the fault tolerance of python3-apt.

[1] https://git.launchpad.net/ubuntu/+source/ubiquity/tree/ubiquity/install_misc.py?h=ubuntu/focal-updates#n534