spec: refactor global nav spec for reliability
spec: refactor global nav spec for reliability

fixes FOO-754
flag = none

test plan:
 - specs pass
 - no flakey flakey

Change-Id: Ie623a27478c49c7ec58ba8e1405fac21ecb9db3c
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/243860
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

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