Fix pcb_clearance list error

[bosd]

Before this pr, setting "plate_pcb_clear": true resulted in:

ValueError: Cannot cut type '<class 'list'>'

screw_insert_all_shapes() Traceback (most recent call last): File "/app/src/dactyl_manuform.py", line 4361, in run() File "/app/src/dactyl_manuform.py", line 4314, in run mod_r, tmb_r = model_side(side="right") File "/app/src/dactyl_manuform.py", line 4104, in model_side shape = difference(shape, [plate_pcb_cutouts(side=side)]) File "/app/src/helpers_cadquery.py", line 89, in difference shape = shape.cut(item) File "/opt/conda/envs/myenv/lib/python3.10/site-packages/cadquery/cq.py", line 3360, in cut raise ValueError("Cannot cut type '{}'".format(type(toCut))) ValueError: Cannot cut type '<class 'list'>'