Speed up user_sees_discussions_navigation_spec.rb

What does this MR do and why?

Describe in detail what your merge request does and why.

Speeds up a spec that was showing up on our top list of slow files.

Before

Finished in 7 minutes 14 seconds (files took 10.85 seconds to load)
19 examples, 0 failures

After

Finished in 1 minute 54.5 seconds (files took 10.47 seconds to load)
19 examples, 0 failures

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MR acceptance checklist

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