ENH: Add img-alt for card and grid-item-card

[jpmckinney]

closes #33
closes #108

[codecov-commenter]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.08 🎉

Comparison is base (d19e589) 89.96% compared to head (fa342ed) 90.05%.

❗ Current head fa342ed differs from pull request most recent head 9db2af4. Consider uploading reports for the commit 9db2af4 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #114      +/-   ##
==========================================
+ Coverage   89.96%   90.05%   +0.08%     
==========================================
  Files          11       10       -1     
  Lines         947      935      -12     
==========================================
- Hits          852      842      -10     
+ Misses         95       93       -2     

Flag	Coverage Δ
pytests	90.05% <100.00%> (+0.08%)	⬆️

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

Impacted Files	Coverage Δ
sphinx_design/grids.py	87.91% <ø> (-0.14%)	⬇️
sphinx_design/cards.py	95.48% <100.00%> (+0.03%)	⬆️

... and 5 files with indirect coverage changes

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[choldgraf]

Missed this one - thanks @jpmckinney , it looks good to me, and appreciate you updating the tests as well 👍