Hello, I was unable to determine the specific license for these game assets. I hope you don't mind me including this in my game. I made some changes to the shotgun sprite and have duly credited you in the game. Here is the link to my game: https://ggbot.itch.io/hellron
Thank you for the credit and good luck on your game! It looks promising and I hope you'll put the assets for good use.
Like I've said in the short description of the assets, I'm giving them away for free so you can use it in any of your FPS projects as you like.
That means commercial, non-commercial use, changing and modifying them at will. There's no need to credit me but it's nice if you do so.