faster probes init

1 job for topic/default/temporal_spectra in 9 minutes and 59 seconds
Status Job ID Name Coverage
  Test
failed #155326
tests

00:09:59

 
Name Stage Failure
failed
tests Test
    Uploading to S3 took 0:00:00.408381
https://codecov.io/github/fluiddyn/fluidsim/commit/15356f1acea011785d23b8855d85c537306f0399
___________________________________ summary ____________________________________
py36: commands succeeded
ERROR: py36-fft: commands failed
codecov: commands succeeded
Running after_script
Uploading artifacts for failed job
ERROR: Job failed: exit code 1