[tox] Do not install Cubicweb 3.27 on Python 2

3 jobs for topic/default/s3-key-pattern in 2 minutes and 47 seconds (queued for 26 seconds)
Status Name Job ID Coverage
  Test
passed flake8 #18288

00:01:12

passed py27 #18289

00:02:47

passed py3 #18290

00:01:55