Create a bad rule that doesn't allow the sandbox to be deleted.

Note that this rule also fails. We make sure that we see both the error from
the rule and the sandbox cleanup.

  $ cat >dune <<EOF
  > (rule
  >  (target foo)
  >  (action (bash "\| touch foo && mkdir bar && touch bar/x && chmod -w bar &&
  >                "\| echo failed action && exit 1
  >           )))
  > EOF

  $ make_dune_project 3.11

  $ dune build ./foo --sandbox=copy 2>&1 | sed -E 's#/.*.sandbox/[^/]+#/.sandbox/$SANDBOX#g'
  File "dune", lines 1-5, characters 0-157:
  1 | (rule
  2 |  (target foo)
  3 |  (action (bash "\| touch foo && mkdir bar && touch bar/x && chmod -w bar &&
  4 |                "\| echo failed action && exit 1
  5 |           )))
  failed action
  [1]

Manual cleaning step so the dune executing the test suite doesn't croak trying
to delete the readonly dir
  $ chmod -R +w _build && rm -rf _build
