Sleep increasing amounts while waiting for uploaded assets to validate

[jwodder]

Closes #405.

[codecov]

Codecov Report

Merging #408 (8ab7973) into master (543e11b) will decrease coverage by 0.09%.
The diff coverage is 44.44%.

@@            Coverage Diff             @@
##           master     #408      +/-   ##
==========================================
- Coverage   81.96%   81.87%   -0.10%     
==========================================
  Files          53       53              
  Lines        5533     5538       +5     
==========================================
- Hits         4535     4534       -1     
- Misses        998     1004       +6     

Flag	Coverage Δ
unittests	81.87% <44.44%> (-0.10%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
dandi/dandiapi.py	85.96% <44.44%> (-2.38%)	⬇️

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[yarikoptic]

I think that should do it, thank you @jwodder !