Inconsistent assetsBuildDirectory path in "build/server/assets/server-build-[hash].js" while nested building in Windows

[adelriosantiago]

Reproduction

-Grab a project with a vite.config.js.
-Build in Windows with buildDirectory: 'build/test' then with buildDirectory: 'build\\test'.
-Both builds at "build/server/assets/server-build-[hash].js" will have the same "assetsBuildDirectory" apth which works only in Windows.
-I would expect the "assetsBuildDirectory" to have "/" like all other lines, instead the file includes:

//...
const mode = "pre-prod";
const assetsBuildDirectory = "artifacts\\test\\client";
const basename = "/";
//...

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (12) x64 AMD Ryzen 5 3600 6-Core Processor
    Memory: 7.72 GB / 15.95 GB
  Binaries:
    Node: 20.13.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.22 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 10.5.2 - C:\Program Files\nodejs\npm.CMD
    pnpm: 9.4.0 - ~\AppData\Roaming\npm\pnpm.CMD
  Browsers:
    Edge: Chromium (128.0.2739.79)
    Internet Explorer: 11.0.19041.4355

Used Package Manager

npm

Expected Behavior

I would expect the builder to keep be buildDirectory: 'build/test', which works both in Windows and Linux.

Actual Behavior

The line is buildDirectory: 'build\\test' when built in Windows, and buildDirectory: 'build/test' (correct) in Linux. The latter one works in Windows and Linux.