[flake8] Fix various errors:

./rql/utils.py:25:    [F401] 'rql._exceptions.BadRQLQuery' imported but unused
./rql/__init__.py:28: [F401] 'rql._exceptions.TypeResolverException' imported but unused
9 jobs for !64 with topic/default/another-experiments in 1 minute and 11 seconds (queued for 5 seconds)
detached
Status Name Job ID Coverage
  Lint
passed black #460562

00:00:26

passed check-manifest #460564

00:00:35

passed flake8 #460561

00:00:29

passed mypy #460563

00:00:35

 
  Tests
failed py3 #460579

00:00:17

failed py3-from-forge #460576

00:00:10

failed py3 #460575

00:00:12

failed py3 #460565

00:00:46

failed py3-from-forge #460566

00:00:30

 
Name Stage Failure
failed
py3 Tests
adding file changes
added 1015 changesets with 2410 changes to 173 files (+8 heads)
new changesets d7a978efc65b:d3779bab121f (27 drafts)

Pulling changeset 2de2f6260eb54250cdbd05288b7470f4a7bf743b...
abort: filtered revision '2de2f6260eb54250cdbd05288b7470f4a7bf743b' (not in 'served' subset)!
pulling from https://gitlab-ci-token:***@forge.extranet.logilab.fr/cubicweb/RQL
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1
failed
py3-from-forge Tests
adding file changes
added 1015 changesets with 2410 changes to 173 files (+8 heads)
new changesets d7a978efc65b:d3779bab121f (27 drafts)

Pulling changeset 2de2f6260eb54250cdbd05288b7470f4a7bf743b...
abort: filtered revision '2de2f6260eb54250cdbd05288b7470f4a7bf743b' (not in 'served' subset)!
pulling from https://gitlab-ci-token:***@forge.extranet.logilab.fr/cubicweb/RQL
Cleaning up file based variables
ERROR: Job failed: command terminated with exit code 1