spec: improve selectors for gradebook filter options
spec: improve selectors for gradebook filter options

flag = none

Change-Id: Iaa21ef83fca311ccc9e282f931286c9f8f49fc6f
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/225862
Reviewed-by: Jeremy Neander <20252aad5efdc666f083d82ab63ed0f9f72a043e@instructure.com>
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
QA-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>
Product-Review: James Butters <4c5a489c9bb72d41f20b3b22aaf4c9b864e32f20@instructure.com>

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