fix: Use manifest-path to override local users

[kratsg]

Some users with pixi.toml in their home directory might have things break due to

 WARN Using local manifest /home/.../pixi.toml rather than /app/pixi.toml from environment variable `PIXI_PROJECT_MANIFEST`
 WARN Encountered 1 warning while parsing the manifest:
  ⚠ The `project` field is deprecated. Use `workspace` instead.
   ╭─[/home/.../pixi.toml:1:1]
 1 │ ╭─▶ [project]
 2 │ │   authors = ["..."]
 3 │ │   channels = ["conda-forge"]
 4 │ │   name = "..."
 5 │ │   platforms = ["linux-64"]
 6 │ ├─▶ version = "0.1.0"
   · ╰──── replace this with 'workspace'
 7 │
   ╰────

Error:   × unknown environment 'ml'

so this fixes it.