Bump @mui/material from 5.15.4 to 6.1.8 in /packages/experiment-manager

Bumps [@mui/material](https://github.com/mui/material-ui/tree/HEAD/packages/mui-material) from 5.15.4 to 6.1.8.
- [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/v6.1.8/packages/mui-material)

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

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

packages/experiment-manager/package.json

@@ -49,7 +49,7 @@
         "@mrblenny/react-flow-chart": "0.0.14",
         "@jupyterlab/translation": "3.5.3",
         "@mui/icons-material": "5.15.14",
-        "@mui/material": "5.15.4",
+        "@mui/material": "6.1.8",
         "d3": "7.8.2",
         "lodash": "4.17.21",
         "prop-types": "15.8.1",