build(deps): Bump @mui/system from 5.15.3 to 5.15.6 (#1476)

Bumps [@mui/system](https://github.com/mui/material-ui/tree/HEAD/packages/mui-system) from 5.15.3 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-system)

---
updated-dependencies:
- dependency-name: "@mui/system"
  dependency-type: indirect
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>