add tests for Omniglot dataset

[pmeier]

No description provided.

[codecov]

Codecov Report

Merging #3461 (0371df2) into master (e9a9493) will increase coverage by 0.23%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3461      +/-   ##
==========================================
+ Coverage   76.16%   76.39%   +0.23%     
==========================================
  Files         105      105              
  Lines        9707     9703       -4     
  Branches     1556     1556              
==========================================
+ Hits         7393     7413      +20     
+ Misses       1834     1808      -26     
- Partials      480      482       +2     

Impacted Files	Coverage Δ
torchvision/datasets/hmdb51.py	28.33% <0.00%> (-66.67%)	⬇️
torchvision/datasets/kinetics.py	40.00% <0.00%> (-56.00%)	⬇️
torchvision/datasets/phototour.py	25.25% <0.00%> (+<0.01%)	⬆️
torchvision/transforms/functional_tensor.py	79.23% <0.00%> (+0.19%)	⬆️
torchvision/models/detection/anchor_utils.py	94.66% <0.00%> (+1.33%)	⬆️
torchvision/datasets/utils.py	72.58% <0.00%> (+2.15%)	⬆️
torchvision/ops/deform_conv.py	72.30% <0.00%> (+3.07%)	⬆️
torchvision/datasets/cifar.py	95.00% <0.00%> (+5.00%)	⬆️
torchvision/io/_video_opt.py	40.11% <0.00%> (+5.08%)	⬆️
torchvision/io/__init__.py	89.65% <0.00%> (+6.89%)	⬆️
... and 3 more

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[datumbox]

LGTM!