[CI] Install the gcc/g++ multilib package for building on 32 bits

Summary:
This is actually missing and causes the linux 32 build to fail.
Also update the cross gcc versions to use the same version (9) as the gitian builds so we are testing under release conditions.

Test Plan:
Tried on a bullseye machine:

./contrib/teamcity/build-configurations.py build-linux32

Fails without that patch, succeeds after.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D12114