mathlib3

84a438e2 - refactor(algebraic_geometry/*): rename structure sheaf to `Spec.structure_sheaf` (#12785)

refactor(algebraic_geometry/*): rename structure sheaf to `Spec.structure_sheaf` (#12785) Following [this Zulip message](https://leanprover.zulipchat.com/#narrow/stream/113488-general/topic/Rename.20.60structure_sheaf.60.20to.20.60Spec.2Estructure_sheaf.60/near/275649595), this pr renames `structure_sheaf` to `Spec.structure_sheaf`