Doc: non-public email is used for commit match

What does this MR do?

Add a note beneath https://docs.gitlab.com/ee/user/profile/#add-emails-to-your-user-profile section specifying "Making your email non-public does not prevent it from being utilised for commit matching."

Related issues

Related to: #428932 (closed)
Original discussion: https://gitlab.com/groups/gitlab-org/-/epics/11880#note_1631634889

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