deps: fix GN build warning in ncrypto

PR-URL: https://github.com/nodejs/node/pull/54222
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

deps/ncrypto/unofficial.gni

@@ -14,6 +14,7 @@ template("ncrypto_gn_build") {
       "-Wno-deprecated-declarations",
       "-Wno-pessimizing-move",
       "-Wno-shadow",
+      "-Wno-unused-variable",
     ]
   }