fix: better warning for download error

[tlambert03]

slightly more informative error when failing to download an iconify icon

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.97%. Comparing base (34b9851) to head (82f3cb4).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
src/superqt/iconify/__init__.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #266   +/-   ##
=======================================
  Coverage   86.97%   86.97%           
=======================================
  Files          46       46           
  Lines        3439     3439           
=======================================
  Hits         2991     2991           
  Misses        448      448           

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