[Bug]: Placeholder class on select not working

[damienroche]

Reproduction

https://www.shadcn-vue.com/docs/components/select#form

Describe the bug

For Select component, the placeholder class isn't working.
On demo page, we can see that Select have a placeholder:text-muted-foreground so when there's no selected value, it should be displayed in the same color as the message below with the same class

System Info

System:
    OS: macOS 14.5
    CPU: (10) arm64 Apple M1 Pro
    Memory: 87.31 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.12.2 - ~/.nvm/versions/node/v20.12.2/bin/node
    Yarn: 1.22.18 - ~/Library/pnpm/yarn
    npm: 10.5.0 - ~/.nvm/versions/node/v20.12.2/bin/npm
    pnpm: 8.10.5 - ~/Library/pnpm/pnpm
    bun: 0.2.1 - ~/.bun/bin/bun
  Browsers:
    Chrome: 130.0.6723.92
    Safari: 17.5
  npmPackages:
    radix-vue: ^1.9.7 => 1.9.7 
    unplugin-auto-import: ^0.18.3 => 0.18.3 
    vue: ^3.5.12 => 3.5.12

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests