Fix noisy_circuit in mitigation module

[MatteoRobbiati]

Fixes the error mitigation execution using qibolab backend.

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (83254d3) 100.00% compared to head (61aae63) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #884   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           48        48           
  Lines         6400      6400           
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  Hits          6400      6400           

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/qibo/models/error_mitigation.py	100.00% <100.00%> (ø)

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[BrunoLiegiBastonLiegi]

Thanks @MatteoRobbiati for spotting and correcting this.

[BrunoLiegiBastonLiegi]

I think there is something wrong in the vnCDR as well. In lines 322-325 we have:

noisy_c = get_noisy_circuit(circuit, level, insertion_gate=insertion_gate)
if noise_model != None and backend.name != "qibolab":
    noisy_c = noise_model.apply(circuit)
circuit_result = backend.execute_circuit(noisy_c, nshots=nshots)

but shouldn't it be noisy_c = noise_model.apply(noisy_c) @AlejandroSopena ?

[AlejandroSopena]

Indeed. Thanks for spotting it @BrunoLiegiBastonLiegi