feat(pnpm): Automagically remove `# Renovate security update: ` after Minimum Release Age has passed

### Describe the proposed change(s).

As suggested in https://github.com/renovatebot/renovate/discussions/40591, it would be useful to "clean up" 

I'm not sure we'd want to do this during "regular" PR updates - as it'll introduce unnecessary noise to PRs - so this should be done during `lockFileMaintenance`