controllers/krate/owners: Remove spawn_blocking() from GET /crates/:crate_id/owner_team endpoint

[eth3lbert]

This converts Team::owning() to an async fn, allowing us to remove the relevant spawn_blocking() usage in the controller.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.01%. Comparing base (c480761) to head (dc7095d).
Report is 4 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9905      +/-   ##
==========================================
- Coverage   89.01%   89.01%   -0.01%     
==========================================
  Files         290      290              
  Lines       30110    30109       -1     
==========================================
- Hits        26803    26801       -2     
- Misses       3307     3308       +1     

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