Purchase a used or new physical copy of Skate 3 for the PS3.
Console manufacturers implement various security measures to ensure that only authorized packages can be installed. This includes digital signatures and hash verification to prevent tampering with the package. skate 3 pkg file link
No. Skate 3 is not natively playable via PKG on PS4/PS5. You can stream it via PS Plus Premium, but that’s not a PKG installation. Purchase a used or new physical copy of Skate 3 for the PS3