use pb setter instead of juce setter in noisegate

[iCorv]

NoiseGate: The init-function wrongly uses JUCEs setter

Problem

After calling NoiseGate(), the parameters passed to init only get set in JUCEs NoiseGate-class and not in the pedalboard NoiseGate-class. This can be easily tested with:

noise_gate = pb.NoiseGate(threshold_db=-40, ratio=10, attack_ms=100, release_ms=100)
noise_gate.__repr__

Output:
>>> <bound method PyCapsule.__repr__ of <pedalboard.NoiseGate threshold_db=0 ratio=0 attack_ms=0 release_ms=0 at 0x4905f00>>

Solution

Use pedalboards NoiseGate setter-function, which in turn also sets the parameter in the downstream JUCE class.

[psobot]

Thanks @iCorv!