message: Avoid the use of P0083R3 std::set::merge
diff: @@ -407,7 +407,13 @@ void TaprootSpendData::Merge(TaprootSpendData other)
  merkle_root = other.merkle_root;
  }
  for (auto& [key, control_blocks] : other.scripts) {
  - scripts[key].merge(std::move(control_blocks));
  + // Once P0083R3 is supported by all our targeted platforms,
  + // this loop body can be replaced with:
  + // scripts[key].merge(std::move(control_blocks));
  + auto& target = scripts[key];
  + for (auto& control_block: control_blocks) {
  + target.insert(std::move(control_block));
  + }
  }
  }
  