fix test for City data creation

[Borda]

What does this PR do?

Fixes #315
Turned out that with the existing cache City datasets is failing

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[codecov]

Codecov Report

Merging #343 into master will increase coverage by 0.09%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #343      +/-   ##
==========================================
+ Coverage   82.32%   82.42%   +0.09%     
==========================================
  Files         100      100              
  Lines        5602     5621      +19     
==========================================
+ Hits         4612     4633      +21     
+ Misses        990      988       -2     

Flag	Coverage Δ
cpu	24.75% <ø> (ø)
pytest	24.75% <ø> (ø)
unittests	81.67% <ø> (+0.09%)	⬆️

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

Impacted Files	Coverage Δ
pl_bolts/utils/arguments.py	96.15% <0.00%> (+0.04%)	⬆️
.../models/autoencoders/basic_vae/basic_vae_module.py	91.66% <0.00%> (+0.08%)	⬆️
pl_bolts/losses/self_supervised_learning.py	77.70% <0.00%> (+0.14%)	⬆️
...ts/models/autoencoders/basic_ae/basic_ae_module.py	88.00% <0.00%> (+0.16%)	⬆️
pl_bolts/models/rl/common/gym_wrappers.py	89.91% <0.00%> (+0.26%)	⬆️
pl_bolts/datasets/imagenet_dataset.py	18.45% <0.00%> (+0.38%)	⬆️
pl_bolts/optimizers/lars_scheduling.py	95.74% <0.00%> (+0.39%)	⬆️
..._bolts/models/self_supervised/moco/moco2_module.py	79.23% <0.00%> (+0.49%)	⬆️
pl_bolts/datasets/ssl_amdim_datasets.py	75.00% <0.00%> (+1.08%)	⬆️
...l_bolts/models/rl/vanilla_policy_gradient_model.py	94.64% <0.00%> (+2.67%)	⬆️

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