chore(ring_theory/hahn_series): emb_domain_add needs only add_monoid, not semiring (#7802)
chore(ring_theory/hahn_series): emb_domain_add needs only add_monoid, not semiring (#7802)

This is my fault, the lemma ended up in the wrong place in #7737





leanprover-community/mathlib,leanprover-community/mathlib