Use fmt::format for LOGWARNING

The format string can be checked at compile time. It will be easier to
transition to `std::format`.

source/scriptinterface/Interface.cpp

@@ -196,7 +196,7 @@ bool warn(JSContext* cx, unsigned int argc, JS::Value* vp)
 	std::wstring str;
 	if (!Script::FromJSVal(rq, args[0], str))
 		return false;
-	LOGWARNING("%s", utf8_from_wstring(str));
+	LOGWARNING("{}", utf8_from_wstring(str));
 	args.rval().setUndefined();
 	return true;
 }