Fix flaky test on AidTaxonomy.create_item/2

[pedro-gutierrez]

Describe the bug

The ci workflow failed last night due to a failing test.

Expected behavior

The ci workflow should run tests that are deterministic.

Screenshots

1) test items create_item/2 with valid data creates an item (Ferry.AidTaxonomyTest)
     test/ferry/aid_taxonomy/aid_taxonomy_test.exs:194
     Assertion with == failed
     code:  assert item.mods == [mod1, mod2]
     left:  [%Ferry.AidTaxonomy.Mod{__meta__: #Ecto.Schema.Metadata<:loaded, "aid__mods">, description: "I let you specify the sizes of things.10", id: 25, inserted_at: ~N[2020-10-13 02:23:02], name: "Size10", type: "integer", updated_at: ~N[2020-10-13 02:23:02], values: #Ecto.Association.NotLoaded<association :values is not loaded>}, %Ferry.AidTaxonomy.Mod{__meta__: #Ecto.Schema.Metadata<:loaded, "aid__mods">, description: "I let you specify the sizes of things.9", id: 24, inserted_at: ~N[2020-10-13 02:23:02], name: "Size9", type: "integer", updated_at: ~N[2020-10-13 02:23:02], values: #Ecto.Association.NotLoaded<association :values is not loaded>}]
     right: [
              %Ferry.AidTaxonomy.Mod{
                __meta__: #Ecto.Schema.Metadata<:loaded, "aid__mods">,
                description: "I let you specify the sizes of things.9",
                id: 24,
                inserted_at: ~N[2020-10-13 02:23:02],
                name: "Size9",
                type: "integer",
                updated_at: ~N[2020-10-13 02:23:02],
                values: #Ecto.Association.NotLoaded<association :values is not loaded>
              },
              %Ferry.AidTaxonomy.Mod{
                __meta__: #Ecto.Schema.Metadata<:loaded, "aid__mods">,
                description: "I let you specify the sizes of things.10",
                id: 25,
                inserted_at: ~N[2020-10-13 02:23:02],
                name: "Size10",
                type: "integer",
                updated_at: ~N[2020-10-13 02:23:02],
                values: #Ecto.Association.NotLoaded<association :values is not loaded>
              }
            ]
     stacktrace:
       test/ferry/aid_taxonomy/aid_taxonomy_test.exs:221: (test)