fix grading period toggle button labeling
fix grading period toggle button labeling

fixes CNVS-35437

test plan:
- go to accounts/1/grading_standards
- on the "Grading Periods" tab create multiple grading period sets
  with unique names
- using a SR, navigate to the toggle buttons on the grading periods
- note that the toggle button references the grading period name

Change-Id: Ic8727cef5df8248ab7d39ba3a1fb404d31d6161a
Reviewed-on: https://gerrit.instructure.com/105954
Tested-by: Jenkins
Reviewed-by: Steven Burnett <a0b450117c5d20a22d5c4d52bb8ae13adee003d8@instructure.com>
QA-Review: Deepeeca Soundarrajan <5bcd4b623f00b7fc2942cd1c65c245b30a48a61f@instructure.com>
Product-Review: Felix Milea-Ciobanu <9384aa226ac9d3237ed0bc52e18ffcb251ee0bf7@instructure.com>

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