software/slapos-sr-testing: install new psycopg2 dependency

This is a dependency of slapos.cookbook[test] since 90650d2c (
recipe/test_postgres: test with a real postgres server, 2021-11-12) and
because we run software schema tests from slapos.cookbook in
software/slapos-sr-testing, we also need the dependency here.
5 jobs for 1.0
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

passed SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP2

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3