fix(server): Gracefully handle getFile ECONNREFUSED when worker network is reconfiguring

[nellh]

This error is seen when the worker backend is restarting and isn't yet routable.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes missing coverage. Please review.

Project coverage is 42.36%. Comparing base (9eab62f) to head (72a8b7c).

Files	Patch %	Lines
packages/openneuro-server/src/handlers/datalad.ts	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3079      +/-   ##
==========================================
- Coverage   42.36%   42.36%   -0.01%     
==========================================
  Files         595      595              
  Lines       37919    37921       +2     
  Branches     1096     1096              
==========================================
  Hits        16064    16064              
- Misses      21643    21645       +2     
  Partials      212      212              

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