nixos/fcitx5: fix quickphrase (#368743)

nixos/modules/i18n/input-method/fcitx5.nix

···
     i18n.inputMethod.fcitx5.addons =
       lib.optionals (cfg.quickPhrase != { }) [
         (pkgs.writeTextDir "share/fcitx5/data/QuickPhrase.mb" (
-          lib.mapAttrsToList (
-            name: value: "${name} ${builtins.replaceStrings [ "\\" "\n" ] [ "\\\\" "\\n" ] value}"
-          ) cfg.quickPhrase
+          lib.concatStringsSep "\n" (
+            lib.mapAttrsToList (
+              name: value: "${name} ${builtins.replaceStrings [ "\\" "\n" ] [ "\\\\" "\\n" ] value}"
+            ) cfg.quickPhrase
+          )
         ))
       ]
       ++ lib.optionals (cfg.quickPhraseFiles != { }) [