Remove a small number of hardcoded passwords in specs

What does this MR do and why?

A continuation of Use random passwords in specs (#360030 - closed)

Our specs use static passwords, many of them are weak. This makes it difficult to create changes which introduce password complexity constraints.

This MR updates a small number of instances where we set weak or hardcoded passwords, to use randomly generated passwords.

This ones a bit of a jumble of specs that didn't neatly fit in to the other buckets I created for #360030 (closed). But smaller MRs get merged faster!

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Related to #360030 (closed)