test_storage: Sandbox psycopg2.errors import instruction where needed

And do not execute them within the debian build (just yet?).

Current build [1] fails because the current debian package python3-psycopg2 (2.7) is too old (we need 2.8 to have the import psycopg2.errors working).

rmadison python3-psycopg2
python3-psycopg2 | 2.5.4+dfsg-1  | oldoldstable | amd64, armel, armhf, i386
python3-psycopg2 | 2.6.2-1       | oldstable    | amd64, arm64, armel, armhf, i386, mips, mips64el, mipsel, ppc64el, s390x
python3-psycopg2 | 2.7.7-1       | stable       | amd64, arm64, armel, armhf, i386, mips, mips64el, mipsel, ppc64el, s390x
python3-psycopg2 | 2.7.7-1       | testing      | arm64, armel, armhf, i386, mips64el, mipsel, ppc64el, s390x
python3-psycopg2 | 2.7.7-1       | unstable     | arm64, armel, armhf, i386, mips64el, mipsel, ppc64el, s390x
python3-psycopg2 | 2.7.7-1+b1    | testing      | amd64
python3-psycopg2 | 2.7.7-1+b1    | unstable     | amd64

According to @olasd, there's a psycopg 2.8.3-1 package in the DPMT repo (indeed -> [2]).

I do not see anything blocking a new package though [3]

So, in the mean time, trying to work around that (i don't like it and i'm not even sure that would work, i do feel the need to try something out ;) [4]

• [1] https://jenkins.softwareheritage.org/view/Debian%20packages/job/debian/job/packages/job/DSTO/job/gbp-buildpackage/69/console

• [2] https://salsa.debian.org/python-team/modules/psycopg2/-/tags/upstream%2F2.8.3

• [3] https://bugs.debian.org/cgi-bin/pkgreport.cgi?pkg=python3-psycopg2;dist=unstable

• [4] But i don't see what'd be the proper way of unstucking this (aside making a new psycopg2 package maybe?)

Test Plan

tox (checking the ci's result)

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Migrated from D1943 (view on Phabricator)