Add dependencies label to Renovate PRs

[c-gerke]

With the new Stalebot config, PRs that go "stale" (not having pushes or interactions for 4+ days) are automatically closed. There is a rule in the config that creates an exception for PRs with the "dependencies" label, and this change will make Renovate automatically add this label to its PRs so they don't get pruned for being stale.

[github-actions]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed in 24 hours if no further activity occurs.
If this change is desirable, please accelerate completing it. If it is not, please close the PR. If you're blocked on something, please ensure there's a reference to this PR in a story on your team's board so the team will follow up, and consider closing the PR for now.
Please do not artificially extend the deadline with a dummy comment. If necessary, provide a status update, such as "this change is being actively tested".
Thank you for your contributions and your collaboration in reducing WIP and cycle time.