nixos/mautrix-telegram: loosen umask to keep `config.json` writable

This is needed because `mautrix-telegram --generate-registration`
appears to need write-access to `config.json` as well.

Closes #135884

nixos/modules/services/misc/mautrix-telegram.nix

@@ -128,7 +128,7 @@ in {
         # https://github.com/tulir/mautrix-telegram/issues/584
         [ -f ${settingsFile} ] && rm -f ${settingsFile}
         old_umask=$(umask)
-        umask 0277
+        umask 0177
         ${pkgs.envsubst}/bin/envsubst \
           -o ${settingsFile} \
           -i ${settingsFileUnsubstituted}