Require dune 2.5 to avoid a bug
https://github.com/ocaml/dune/issues/3252 causes 0install-solver to fail
to install, with:
# File "src/tests/dune", line 3, characters 10-23:
# 3 | (deps %{bin:0install})
# ^^^^^^^^^^^^^
# Error: Program 0install not found in the tree or in PATH