Unexpected error using message: {msg, opts} option in validation code

I’ve been trying to use the {msg, opts} tuple variant of the :message option in validate_format, taking a validation that looked like this:

|> validate_format(:field, ~r/some_regex/, message: "oh no!")

to this

|> validate_format(:field, ~r/some_regex/, message: {"oh no!", [error_type: :some_error_type]})

but when I do, I start to get errors that look like this in my validation code:

     ** (EXIT from #PID<0.2412.0>) an exception was raised:
     
          ** (FunctionClauseError) no function clause matching in anonymous fn/1 in Ecto.Changeset.validate_change/3

          The following arguments were given to anonymous fn/1 in Ecto.Changeset.validate_change/3:

              # 1
              {:field, {{"oh no!", [error_type: :some_error_type]}, [validation: :format]}}

          stacktrace:
            (ecto 3.11.2) lib/ecto/changeset.ex:2430: anonymous fn/1 in Ecto.Changeset.validate_change/3
            (elixir 1.16.2) lib/enum.ex:1700: Enum."-map/2-lists^map/1-1-"/2
            (ecto 3.11.2) lib/ecto/changeset.ex:2430: Ecto.Changeset.validate_change/3

Am I misunderstanding how the tuple variant for the :message option is supposed to look? I can’t figure out why this error is happening.