Bump @mui/icons-material from 5.15.20 to 5.15.21 in /webui

Bumps [@mui/icons-material](https://github.com/mui/material-ui/tree/HEAD/packages/mui-icons-material) from 5.15.20 to 5.15.21.
- [Release notes](https://github.com/mui/material-ui/releases)
- [Changelog](https://github.com/mui/material-ui/blob/v5.15.21/CHANGELOG.md)
- [Commits](https://github.com/mui/material-ui/commits/v5.15.21/packages/mui-icons-material)

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

Signed-off-by: dependabot[bot] <support@github.com>

webui/package.json

@@ -13,7 +13,7 @@
     "@emotion/react": "^11.11.4",
     "@emotion/styled": "^11.11.5",
     "@fontsource/inter": "^5.0.18",
-    "@mui/icons-material": "^5.15.20",
+    "@mui/icons-material": "^5.15.21",
     "@mui/material": "^5.15.20",
     "i18next": "^23.11.5",
     "i18next-browser-languagedetector": "^8.0.0",