Ensure generic pack contents have suitable permissions

I know, but like I mentioned before, my CurseForge API key keeps getting limited and the downloads stop, so that AutoForge isn't working for me.
Thats why I'm using the generic setup. But anyway, we might have found the solution to what was going on. Basically the server-files.zip of ATM 10 has very weird permissions inside (version 2.8 and 2.9). Basically the whole content of the zip in 2.7 is writable and 2.8+2.9 had files that were read only.

So it would be awesome if you could add something like this: when you unzip the server files in your script you `chmod 755` them so any weirdness with permissions being carried over can be prevented, at least if that doesn't cause any security implications.

Otherwise the user has to manually unzip -> change permission -> zip -> copy into the downloads folder again

_Originally posted by @fab0912 in https://github.com/itzg/docker-minecraft-server/discussions/3204#discussioncomment-11652622_

The issue does not name a file or test; start by locating the generic setup's server-files.zip extraction path and inspect how permissions are handled. Done means extracted generic pack contents have suitable writable permissions and the affected ATM 10 server files can be used without manually changing and repacking them.

Written by the indexing model from the issue text.