Replace deprecated getPassword()

[offa]

Replaces the deprecated call to getPassword().

Testing done

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[sghill]

Thanks for this contribution!

Looks like this method has been deprecated since jenkinsci/jenkins@f103b78, first included in Jenkins 2.222.1 (March 2020). I think it'd be a good candidate for an automated refactoring recipe in OpenRewrite/rewrite-jenkins if you wanted to apply this more broadly.