bitwarden_rs: fix darwin build

pkgs/tools/security/bitwarden_rs/default.nix

···
 { lib, stdenv, rustPlatform, fetchFromGitHub, nixosTests
 , pkg-config, openssl
-, Security, CoreServices
+, libiconv, Security, CoreServices
 , dbBackend ? "sqlite", libmysqlclient, postgresql }:
 
 let
···
 
   nativeBuildInputs = [ pkg-config ];
   buildInputs = with lib; [ openssl ]
-    ++ optionals stdenv.isDarwin [ Security CoreServices ]
+    ++ optionals stdenv.isDarwin [ libiconv Security CoreServices ]
     ++ optional (dbBackend == "mysql") libmysqlclient
     ++ optional (dbBackend == "postgresql") postgresql;