🐛 FIX: slurm resource validation

[chrisjsewell]

fixes #4530

I also added resource validation tests and moved most of the tests to pytest from unittest (would have been all, but I didn't find a good replacement for AssertLogs)

[codecov]

Codecov Report

Merging #4555 (144bb1e) into develop (ac4c881) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop    #4555      +/-   ##
===========================================
+ Coverage    79.50%   79.51%   +0.01%     
===========================================
  Files          482      482              
  Lines        35326    35327       +1     
===========================================
+ Hits         28081    28085       +4     
+ Misses        7245     7242       -3     

Flag	Coverage Δ
django	73.68% <100.00%> (+0.01%)	⬆️
sqlalchemy	72.84% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
aiida/schedulers/plugins/slurm.py	62.85% <100.00%> (+0.83%)	⬆️
aiida/engine/daemon/runner.py	82.76% <0.00%> (+3.45%)	⬆️

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[sphuber]

Looks good to me. Thanks @chrisjsewell