mathlib3

cacc297c - fix(tactic/norm_num): remove unnecessary argument to rat.cast_zero (#4682)

fix(tactic/norm_num): remove unnecessary argument to rat.cast_zero (#4682) See [Zulip thread](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/.60norm_num.60.20error.20message).