chore: upgrade vitest to 3.0.6 (#9337)

https://linear.app/unleash/issue/2-3296/upgrade-vitest

Follow-up to #9212

The ☝️ PR was failing some tests because `chartjs-adapter-date-fns` is
imported as a [side
effect](https://stackoverflow.com/questions/41127479/es6-import-for-side-effects-meaning)
and seems to be CommonJS-only. When Vitest loads it, it fails to find
named exports (like `_adapters`). By inlining `chartjs-adapter-date-fns`
in our Vitest test config, esbuild transforms it into a proper ES module
for testing.

Additionally, we’re upgrading from v1.4.0 to v3.0.6 directly since our
code seems to be fully compatible.
>Vitest requires Vite >=v5.0.0 and Node >=v18.0.0

frontend/package.json

@@ -124,7 +124,7 @@
     "vite-plugin-env-compatible": "2.0.1",
     "vite-plugin-svgr": "3.3.0",
     "vite-tsconfig-paths": "4.3.2",
-    "vitest": "1.4.0",
+    "vitest": "3.0.6",
     "whatwg-fetch": "3.6.20"
   },
   "resolutions": {

frontend/vite.config.mts

@@ -22,6 +22,11 @@ const vitestConfig = vitestDefineConfig({
         setupFiles: 'src/setupTests.ts',
         environment: 'jsdom',
         exclude: [...configDefaults.exclude, '**/cypress/**'],
+        server: {
+            deps: {
+                inline: ['chartjs-adapter-date-fns'],
+            },
+        },
     },
     css: {
         preprocessorOptions: {