Bump @mui/material-nextjs from 5.16.6 to 6.1.6

Bumps [@mui/material-nextjs](https://github.com/mui/material-ui/tree/HEAD/packages/mui-material-nextjs) from 5.16.6 to 6.1.6.
- [Release notes](https://github.com/mui/material-ui/releases)
- [Changelog](https://github.com/mui/material-ui/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mui/material-ui/commits/v6.1.6/packages/mui-material-nextjs)

---
updated-dependencies:
- dependency-name: "@mui/material-nextjs"
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>