Bump @mui/styles from 5.8.3 to 5.15.6

Bumps [@mui/styles](https://github.com/mui/material-ui/tree/HEAD/packages/mui-styles) from 5.8.3 to 5.15.6.
- [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/v5.15.6/packages/mui-styles)

---
updated-dependencies:
- dependency-name: "@mui/styles"
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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