`cabal-tests --with-cabal` should have sensible default

As suggested in https://github.com/haskell/cabal/pull/8392#issuecomment-1218463229, the result of `cabal list-bin cabal-install` should be the default for `--with-cabal` (rather than skipping all tests that require cabal-install).

In general, a `--with-PROG` should only overwrite _an existing default_ for `PROG`, at least that is the custom (followed by `configure` and `cabal`).