Retry IRDB downloads

[hugobuddel]

This is a bit hackish workaround around our server not sending enough bytes

[hugobuddel]

Annoying thing is that we don't have a reliable way to reproduce this ContentTooShortError exception.

I did notice that usually it is only missing a few bytes, like 20kb max. It seems to never stop halfway through.

[codecov]

Codecov Report

Patch coverage: 61.53% and project coverage change: -0.01 ⚠️

Comparison is base (79d0aea) 75.41% compared to head (8b27a63) 75.40%.

Additional details and impacted files

@@              Coverage Diff               @@
##           dev_master     #232      +/-   ##
==============================================
- Coverage       75.41%   75.40%   -0.01%     
==============================================
  Files             149      149              
  Lines           15283    15293      +10     
==============================================
+ Hits            11525    11532       +7     
- Misses           3758     3761       +3     

Impacted Files	Coverage Δ
scopesim/server/database.py	71.05% <61.53%> (-0.06%)	⬇️

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[teutoburg]

We should probably find a better solution for that in the future, but I'm fine with trying this for now. FYI, I've been working on the whole download module over the last few days, let's discuss later today.

[hugobuddel]

A better solution is fine with me. The CI now only fails during the nightly run I believe, so maybe it is not so problematic to keep it red for a bit longer

[hugobuddel]

Closing in favor of #234