ci: fix tests

- flask docu on readthedocs is no longer available
- use beta tags for autoscale runners
12 jobs for fix-tests in 13 minutes and 45 seconds (queued for 3 seconds)
Status Name Job ID Coverage
  Test
passed py3.5-min-mysql #16404
beta

00:11:22

92.0%
passed py3.5-min-postgresql #16405
beta

00:11:30

92.0%
passed py3.5-min-sqlite #16406
beta

00:11:22

91.0%
passed py3.5-pypi-mysql #16407
beta

00:13:07

92.0%
passed py3.5-pypi-postgresql #16408
beta

00:11:27

92.0%
passed py3.5-pypi-sqlite #16403
beta

00:11:53

91.0%
canceled py3.5-min-mysql #16401
beta

00:04:52

canceled py3.5-min-postgresql #16399
beta

00:04:53

canceled py3.5-min-sqlite #16397
beta

00:04:54

canceled py3.5-pypi-mysql #16402
beta

00:04:52

canceled py3.5-pypi-postgresql #16400
beta

00:04:53

canceled py3.5-pypi-sqlite #16398
beta

00:04:53