mathlib3

5c4b3d41 - chore(ring_theory/adjoin_root): modify `field` instance on `adjoin_root` (#19119)

chore(ring_theory/adjoin_root): modify `field` instance on `adjoin_root` (#19119) We copy the fields of `group_with_zero` instead of `field`. This speeds up the already ported `adjoin_root/AdjoinRoot` pair. [Zulip discussion](https://leanprover.zulipchat.com/#narrow/stream/287929-mathlib4/topic/!4.234339.20.20FieldTheory.2ESplittingField)