Drop support for older GHCs

[phadej]

With GHC-9.14 we'll support 13 major GHCs. That's quite many CI jobs. I think keeping it at around 10 (~5 years worth of GHCs) should more than enough.

[arybczak]

I'd drop support for <8.10, this is what I have in most of my packages (starting to slowly move towards dropping <9.2) and no one seems to complain 🤔