Fix go-to-epics link

What does this MR do and why?

Updates the go-to-epics method to always look under Plan for the Epics link. Previously we were expecting the test user to have Epics under Pinned but that can easily get unpinned and break tests.

Fixes: #461695 (closed)

Epic link we're using before fix:	Epic link we're using after fix:

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