Fix release dist to include static binaries
Previously, the release distributions included the dynamic (rather than statically-built) binaries. There was a subtle bug that caused the static haskell.nix project to be ignored and use the default (dynamic). It was introduced by b6a024ce7bd1a54efa7c8e5741e40e82fbdd2736. Fixes: #2108 See also: PR #1962