chore: upgrade Vitest 4.1.0-beta.6

[react-server-bot]

Automated daily upgrade of Vite, Rolldown, and/or Vitest to the latest available versions.

Vitest: 4.1.0-beta.5 → 4.1.0-beta.6

Updated locations

• packages/react-server/package.json — vite, rolldown
• test/package.json — vite, rolldown, vitest, @vitest/ui
• packages/rsc/package.json — vitest, @vitest/*
• packages/create-react-server/test/package.json — vitest
• package.json — all pnpm.overrides for Vite
• pnpm-lock.yaml

Smoke test

• Dev mode — hello world test passed ✅
• Build+start mode — hello world test passed ✅

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (main@4b8cccb). Learn more about missing BASE report.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #340   +/-   ##
=======================================
  Coverage        ?   94.24%           
=======================================
  Files           ?        2           
  Lines           ?     2224           
  Branches        ?      669           
=======================================
  Hits            ?     2096           
  Misses          ?      128           
  Partials        ?        0           

Flag	Coverage Δ
rsc	94.24% <ø> (?)

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