Use virtualenv for CI tests

3 jobs from gajim_1.1 in 4 minutes and 18 seconds (queued for 2 minutes and 48 seconds)
Status Job ID Name Coverage
  Test
passed #9181
run-appdata

00:00:05

passed #9180
run-tests

00:04:02

 
  Build
passed #9182
run-build

00:00:10