arg typoo in BSHR operator

[palatinb]

Short description	arg typoo in BSHR operator
Expected operation	a should be replaced by arg
Experienced operation	Stops running the program
Reproductive steps	After running the bit_shift_right operator, the program stops working
Error location	test-automation-engineer-python-junior/icalc.py Line 57 in 51760f9 def do_bit_shift_right(self, a):
Test result	Not OK
Priority	High