css url() after legacy build generate __VITE_ASSET__hash in legacy.js file

[yanglei00]

Describe the bug

vite@3.0.4、 @vitejs/plugin-legacy@2.0.0 用url()引入背景图，在build后legacy.js文件里的__VITE_ASSET__hash没有被替换掉

Reproduction

https://github.com/yanglei00/vite-bug-report

System Info

System:
    OS: macOS 12.2.1
    CPU: (8) arm64 Apple M1
    Memory: 63.28 MB / 16.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.13.1 - ~/.nvm/versions/node/v16.13.1/bin/node
    Yarn: 1.22.17 - ~/.nvm/versions/node/v16.13.1/bin/yarn
    npm: 8.1.2 - ~/.nvm/versions/node/v16.13.1/bin/npm
  Browsers:
    Chrome: 104.0.5112.79
    Chrome Canary: 106.0.5218.0
    Firefox: 99.0.1
    Safari: 15.3
  npmPackages:
    @vitejs/plugin-legacy: ^2.0.0 => 2.0.0 
    @vitejs/plugin-vue: ^3.0.1 => 3.0.1 
    vite: ^3.0.4 => 3.0.4

Used Package Manager

pnpm

Logs

1. pnpm build
2. dist/assets/index-legacy.54087a6e.js文件中搜索__VITE_ASSET__

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• 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.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

Duplicate of #9246