mathlib3

d2140efb - feat(algebra/gcd_monoid): `gcd_mul_dvd_mul_gcd` (#4386)

feat(algebra/gcd_monoid): `gcd_mul_dvd_mul_gcd` (#4386) Adds a `gcd_monoid` version of `nat.gcd_mul_dvd_mul_gcd` Co-authored-by: Aaron Anderson <65780815+awainverse@users.noreply.github.com>