Module __mocks__ in pnpm monorepo doesn't work for workspace packages

Describe the bug

We've encountered a problem in our pnpm monorepo when __mocks__ folder module automocking doen't work for packages that are imported from pnpm workspace rather than npm registry.

When we try to import a package from NPM registry as usual, it works fine, but importing the same package as "workspace:*" in package.json leads to vitest silently ignoring __mocks__ folder based mocks.

Reproduction

StackBlitz: https://stackblitz.com/~/github.com/Koka/vitest_pnpm_problem

What you can see there is a tiny pnpm monorepo with three packages: package_one - a thing we're importing and mocking, and package_two and package_three which both import first package and mock it using __mocks__ folder.

Package two imports first package from pnpm workspace, and package three imports first package from NPM registry.

Despite latter packages do the very same thing in an exactly same setup, tests for package_two are failing because mock wasn't successful.

System Info

System:
    OS: macOS 15.3.1
    CPU: (12) arm64 Apple M3 Pro
    Memory: 4.77 GB / 36.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.10.0 - ~/.nvm/versions/node/v20.10.0/bin/node
    npm: 10.2.3 - ~/.nvm/versions/node/v20.10.0/bin/npm
    pnpm: 8.6.12 - ~/Library/pnpm/pnpm
  Browsers:
    Safari: 18.3

Used Package Manager

pnpm

Validations

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• Read the Contributing Guidelines.
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• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.

Start with the StackBlitz reproduction and compare package_two, which imports the workspace package and has failing tests, with package_three, which imports the registry package and passes. Trace how Vitest discovers mocks for each package setup; done means workspace:* imports honor the same folder-based automocking behavior as registry imports.