The issues underlying #6173 prompted me to look into which `find`
version we had in dev-env, and I was surprised to notice we had none. We
already have `findutils` in our nix configuration, however, so this is
just adding the symlink.
Note that, on my machine at least, switching from the macOS-provided one
to the dev-env one does not change the result order for the hash
calculation in `ci/patch_bazel_windows`, so this would likely not have
helped for #6173. Still, we use `find` in many places in our scripts so
I think it's worth having there.
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