fix(vitest): disable optimizer by default until it's stable

[sheremet-va]

Description

The optimizer is not stable enough at this point (some packages like react don't work with it and if all dependencies are not pre-bundled, there is a high chance users will get a "Cannot find module" error only in CI which is hard to debug). Since Vitest 1.3.0 focuses more on stability, we are disabling this option until we can figure out a good way to enable it without these hazards. If your tests are slower after this PR, you can always enable optimizer manually:

export default defineConfig({
  test: {
    deps: {
      optimizer: {
        web: {
           enabled: true,
        },
        ssr: {
          enabled: true,
        }
      }
    }
  }
})

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[hi-ogawa]

Sounds good to me. Considering the issue with ssr.optimizeDeps #4910 is fixed since Vite 5.1 vitejs/vite#15561, I think this affects jsdom/happy-dom use cases mostly.