[small] pytorch readonly error bug fix

[verbose-void]

please also review #1024 as this branch is based on it and they're both really small

if you tried to use pytorch on a dataset in readonly mode it would fail. this fixes it and adds a test for future proof

[AbhinavTuli]

Minor change required.

[codecov]

Codecov Report

Merging #1026 (80571bb) into main (94b43ea) will increase coverage by 0.00%.
The diff coverage is 90.90%.

@@           Coverage Diff           @@
##             main    #1026   +/-   ##
=======================================
  Coverage   88.61%   88.61%           
=======================================
  Files          86       87    +1     
  Lines        3916     3936   +20     
=======================================
+ Hits         3470     3488   +18     
- Misses        446      448    +2     

Impacted Files	Coverage Δ
hub/util/dataset.py	66.66% <66.66%> (ø)
hub/integrations/pytorch.py	80.48% <100.00%> (+0.11%)	⬆️
hub/integrations/pytorch_old.py	85.41% <100.00%> (+0.31%)	⬆️
hub/integrations/tests/test_pytorch.py	82.60% <100.00%> (+1.65%)	⬆️

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