fix Resources.__str__ to match attribute names

[Qottmann]

Minor thing:
The resources repr and attribute names dont coincide, e.g.

>>> U = qml.TrotterProduct(qml.X(0) + qml.Y(0), time=0.5, n=2, order=2)
>>> U.resources()
wires: 1
gates: 8
depth: 8
shots: Shots(total=None)
gate_types:
{'Exp': 8}
gate_sizes:
{1: 8}

I would e.g. expect to be able to obtain the number of gates but neither U.resources().gates nor U.resources()["gates"] or getattr(U.resources(), "gates") work - because the attribute is actually called num_gates.

This PR just fixes the str representation to match the attribute name.
This is such a minor thing that it was easier and faster to just fix it than open an issue / sc story 😬

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.29%. Comparing base (bf03136) to head (e5f1398).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6581      +/-   ##
==========================================
- Coverage   99.30%   99.29%   -0.01%     
==========================================
  Files         454      454              
  Lines       43269    43267       -2     
==========================================
- Hits        42967    42964       -3     
- Misses        302      303       +1     

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[Jaybsoni]

Nice catch! Although I know we have lots of docstrings and documentation where we have hand-written the output of printing a resources object. You will need to track those instances down to complete the update 😢.

Thanks for the fix!

[Qottmann]

Good point, thanks @Jaybsoni . Wasnt as bad, updated it ✅