Expected Behavior

When using lang dune 3.6 instead of lang dune 2.0, staged_pps should still work.

Actual Behavior

The build process fails with the following error:

File "dune", line 1, characters 0-81:
1 | (executable
2 |  (name proj)
3 |  (preprocess (staged_pps ppx_import ppx_deriving.show)))
Error: This rule forbids all sandboxing modes (but it also requires
sandboxing)

Reproduction

1. Create dune-project with the following contents:

   (lang dune 3.6)
   (name proj)
   

2. Create dune with the following contents:

   (executable
    (name proj)
    (preprocess (staged_pps ppx_import ppx_deriving.show)))
   

3. Create an empty proj.ml.
4. Run dune build.

Specifications

• Version of dune (output of dune --version): 3.6.1
• Version of ocaml (output of ocamlc --version): 4.14.0
• Operating system (distribution and version): Arch Linux