Ecto 3 put_embed not accepting structs?

In upgrading from Ecto 2 to Ecto 3 I’m dealing with a failing test. If I use ExMachina build(:address) I’ll get an error trying to put_embed/3:

** (ArgumentError) unknown field `:__meta__` in %Orders.Schemas.InlineAddress{address: #Ecto.Association.NotLoaded<association :address is not loaded>, address_id: nil, city: nil, country_code: nil, delivery_instructions: nil, full_name: nil, id: nil, inserted_at: nil, line1: nil, line2: nil, override: nil, phone_number: nil, sap_id: nil, state_or_region: nil, type: nil, updated_at: nil, version: 1, zip_code: nil}
     code: exec(order: order, send_email: send_email_mock, send_csv: send_csv_mock, csv: true)
     stacktrace:
       (ecto 3.6.2) lib/ecto/changeset.ex:1225: Ecto.Changeset.put_change/7
       (stdlib 3.17) maps.erl:410: :maps.fold_1/3
       (ecto 3.6.2) lib/ecto/changeset.ex:396: Ecto.Changeset.change/2
       (ecto 3.6.2) lib/ecto/changeset/relation.ex:198: Ecto.Changeset.Relation.do_change/4
       (ecto 3.6.2) lib/ecto/changeset/relation.ex:326: Ecto.Changeset.Relation.single_change/5
       (ecto 3.6.2) lib/ecto/changeset/relation.ex:165: Ecto.Changeset.Relation.change/3
       (ecto 3.6.2) lib/ecto/changeset.ex:1213: Ecto.Changeset.put_change/7
       (ecto 3.6.2) lib/ecto/changeset.ex:1423: Ecto.Changeset.put_relation/5
       (packsize_data 0.0.1) ...accounting/schemas/vendor_po.ex:52: Accounting.VendorPO.changeset/2

vendor_po.ex referenced looks like:

  def changeset(%VendorPO{} = po, attrs) do
    po
    |> cast(attrs, ~w[customer_po_number]a)
    |> put_embed_from_params(:shipping_address)
  end

  defp put_embed_from_params(changeset, key) do
    put_embed(changeset, key, changeset.params["#{key}"])
  end

Changing the test to params_for(:address) works. I don’t see anything in the Ecto docs that indicates something changed, to the contrary the documentation for put_assoc/3 states:

changesets or structs - when a changeset or struct is given, they are treated as the canonical data and the associated data currently stored in the association is ignored.