Update Mod to 1.21.8

That leaves the obvious final question of "where is 1.21.5, and what are you planning for 1.22?" The answer is: I need a break from porting this mod. I've had to dedicate a substantial amount of time to port to minor updates while ultimately throwing out that code due to future changes. This isn't sustainable and it's taken time away from being able to work on new features (case in point - most ModernFix features on 1.20 are just ports of code developed during the 1.19 lifecycle).
Whether or not it's better to port to the latest versions as they come out or stick to a quasi-"LTS" is a hotly contested topic in the community. But for ModernFix specifically, I think the latter is more beneficial to the playerbase overall, so I'm simply not going to be porting to 1.21.5 or any of the minor versions until I see the community settle on a new version for modpacks. The code is as always open source, so others are free to port to those minor versions if they're interested, and I won't stop them.

stole this from #547

Closing as a duplicate of #547