[browser] mocking + cacheDir fails for some cacheDirs

[meesvandongen]

Describe the bug

When using vitest browser mode, mocking does not work if cacheDir is set to a subparent directory.
This DOES work properly in node mode.

Reproduction

https://github.com/meesvandongen/vitest-repro

npm run test:child:browser // success
npm run test:parent:browser // fails
npm run test:parent:node // success

System Info

browser = chrome, playwright; did not test with other setups

  System:
    OS: macOS 15.1
    CPU: (16) arm64 Apple M3 Max
    Memory: 7.45 GB / 64.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.11.0 - ~/.nvm/versions/node/v22.11.0/bin/node
    npm: 10.9.0 - ~/.nvm/versions/node/v22.11.0/bin/npm
    pnpm: 9.4.0 - /opt/homebrew/bin/pnpm
    bun: 1.1.31 - ~/.bun/bin/bun
  Browsers:
    Chrome: 131.0.6778.69
    Edge: 131.0.2903.48
    Safari: 18.1
  npmPackages:
    @vitest/browser: ^2.1.5 => 2.1.5

Used Package Manager

npm

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