src: fix error handling in ExportJWKAsymmetricKey

Because call sites check IsNothing() on the return value of
ExportJWKAsymmetricKey() and ignore the boolean value if the return
value is Just (i.e., not nothing), this function must return Nothing()
instead of Just(false) when throwing a JavaScript error.

PR-URL: #53767
Reviewed-By: Filip Skokan <panva.ip@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz.nizipli@sentry.io>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: tniessen

src/crypto/crypto_keys.cc

@@ -505,7 +505,7 @@ Maybe<bool> ExportJWKAsymmetricKey(
     case EVP_PKEY_X448: return ExportJWKEdKey(env, key, target);
   }
   THROW_ERR_CRYPTO_JWK_UNSUPPORTED_KEY_TYPE(env);
-  return Just(false);
+  return Nothing<bool>();
 }
 
 std::shared_ptr<KeyObjectData> ImportJWKAsymmetricKey(