virtual file system is broken in v6

[himself65]

Describe the bug

import { createServer } from 'vite'

const server = await createServer({
  plugins: [
    {
      name: 'virtual-fs',
      resolveId (id) {
        if (id === 'my-virtual-file') {
          return id + '.js'
        }
      },
      load (id) {
        if (id === 'my-virtual-file.js') {
          return 'export default "Hello, world!"'
        }
      }
    }
  ]
})

console.log(await server.ssrLoadModule('my-virtual-file.js'))

await server.close()

This is working in v5, but broken in v6.

Reproduction

https://stackblitz.com/edit/stackblitz-starters-prwdrf?file=index.js

Steps to reproduce

No response

System Info

N/A

Used Package Manager

npm

Logs

No response

Validations

• [X] Follow our Code of Conduct
• [X] Read the Contributing Guidelines.
• [X] Read the docs.
• [X] Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• [X] Make sure this is a Vite issue and not a framework-specific issue. For example, if it's a Vue SFC related bug, it should likely be reported to vuejs/core instead.
• [X] Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• [X] The provided reproduction is a minimal reproducible example of the bug.

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• stackblitz-starters-prwdrf (Open reproduction)