Update vitest monorepo to v4

Author: renovate[bot]

package.json

@@ -74,7 +74,7 @@
     "@typescript-eslint/parser": "^8.0.0",
     "@vector-im/compound-design-tokens": "^6.0.0",
     "@vitejs/plugin-react": "^5.0.0",
-    "@vitest/coverage-v8": "^3.2.4",
+    "@vitest/coverage-v8": "^4.0.0",
     "browserslist-to-esbuild": "^2.0.0",
     "eslint": "^8.49.0",
     "eslint-config-prettier": "^10.0.0",
@@ -98,7 +98,7 @@
     "typescript": "^5.2.2",
     "vite": "^7.0.3",
     "vite-plugin-dts": "^4.5.4",
-    "vitest": "^3.2.4"
+    "vitest": "^4.0.0"
   },
   "dependencies": {
     "@floating-ui/react": "^0.27.0",