build(nix): Fix static checks

Author: sgillespie

flake.nix

@@ -76,6 +76,15 @@
                     schema = ./schema;
                   })
 
+                (final: prev: {
+                  fourmolu = final.haskell-nix.tool "ghc96" "fourmolu" {
+                    version = "latest";
+                  };
+
+                  hlint = final.haskell-nix.tool "ghc96" "hlint" {
+                  };
+                })
+
                 (final: prev: {
                   postgresql = prev.postgresql.overrideAttrs (_:
                     final.lib.optionalAttrs (final.stdenv.hostPlatform.isMusl) {