Password field with the dual flag and an array in append keeps appending buttons

I think that the [Password field](https://elastic.github.io/eui/#/forms/form-controls) passes the `append arrays` by reference, when used with the dual flag it keeps appending new buttons.

We discovered this issue after migrating a similar custom component to the EUI feature introduced in this PR #3751. This is not a blocking issue, a work around is to use a `ReactElement` in the `append` key.