Adjust update_runners_registration_token permission

What does this MR do and why?

Related to #341311 (closed)

There was an inconsistency detailed in #341311 (comment 684599010) with the update_runners_registration_token permission that's used when resetting the runner registration token.

This MR makes requires group owner role for update_runners_registration_token instead of group maintainer to better align with all other runner operations.

Screenshots or screen recordings

N/A

How to set up and validate locally

curl --header "Private-Token: $TOKEN" "http://localhost:3000/api/v4/groups/$GROUPID/runners/reset_registration_token"

It should fail with a group maintainer token and succeed with a group owner token.

MR acceptance checklist

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