Add missing spec for promote label modal

Rinku Crequested to merge
gitlab-community/gitlab-org/gitlab:feat/add-missing-spec-for-promote-label-modal into master

What does this MR do and why?

Add missing spec for promote label modal to ensure right params are passed while calling the promote label api

References

Follow-up from : !211379 (merged)

Screenshots or screen recordings

Before After
Edited by Rinku C

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