fix: upgrade @mui/material from 5.15.19 to 5.15.21

Snyk has created this PR to upgrade @mui/material from 5.15.19 to 5.15.21.

See this package in npm:
@mui/material

See this project in Snyk:
https://app.snyk.io/org/goliathlabs/project/ee1e0edd-da27-4ea4-adde-fedab2136607?utm_source=github&utm_medium=referral&page=upgrade-pr

Author: snyk-bot

website/package-lock.json

@@ -12,7 +12,7 @@
     "@emotion/styled": "^11.11.5",
     "@mui/icons-material": "^5.15.21",
     "@mui/lab": "^5.0.0-alpha.166",
-    "@mui/material": "^5.15.19",
+    "@mui/material": "^5.15.21",
     "@mui/styles": "^5.15.21",
     "common-tags": "^1.8.2",
     "date-fns": "^3.6.0",