Expected Behavior

Diffing expected tests when patdiff is not installed (git diff is used) works

Actual Behavior

Diffing with git diff doesn't work because the sandboxing create a symlink and git diff is configured to not follow symlink

Reproduction

1. check that patdiff is not installed
2. make a modification in a test of dune
3. run make test

Specifications

• Version of dune (output of dune --version): master a6fa067
• Version of ocaml (output of ocamlc --version): 4.09
• Operating system (distribution and version): ubuntu 20.03