Update reviewers for vitess dep upgrade PRs

[mattlord]

The workflow was now failing because Manan is no longer a contributor:

Create or update the pull request
  Attempting creation of pull request
  Created pull request #762 (planetscale:create-pull-request/patch => main)
  Requesting reviewers 'frouioui,GuptaManan100'
  Error: Reviews may only be requested from collaborators. One or more of the users or teams you specified is not a collaborator of the planetscale/vitess-operator repository. - https://docs.github.com/rest/pulls/review-requests#request-reviewers-for-a-pull-request

The workflow now passes in the PR branch: https://github.com/planetscale/vitess-operator/actions/runs/23019342016/job/66851198675