worker/jobs/archive_version_downloads: Reduce spawn_blocking() usage

[Turbo87]

We can use diesel-async instead :)

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 5 lines in your changes missing coverage. Please review.

Project coverage is 88.72%. Comparing base (227da83) to head (8808af0).
Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
src/worker/jobs/archive_version_downloads.rs	85.71%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9699      +/-   ##
==========================================
+ Coverage   88.71%   88.72%   +0.01%     
==========================================
  Files         287      287              
  Lines       29336    29338       +2     
==========================================
+ Hits        26026    26031       +5     
+ Misses       3310     3307       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.