Hi Marco,
I'm afraid that there's not a practical solution for this.
While this tool is designed by Google, it's not being selective of the nature of the conflict. In other words, it's a bad practice to load resources with short expiration time so it's just pointing you that you've got 3 scripts that fail on that general rule.
My advice here is the following: ignore the recommendation and improve everything else that you can actually improve.
Just if you're really sure about what you're doing, there's a workaround that may work in some cases. I don't recommend it though but it's up to you.
You can save some of those scripts on your remote server and instead of pointing to google's ones use yours with a longer expiration time.
Again, I'd just let it go and keep using google scripts as is and improve other aspects of the site.
Best regards,
Carlos.