copilot: Update version of GHC in README. Refs #590.

Copilot is currently able to work with GHC 9.10, but the README still indicates
that it is compatible with versions up to 9.8.

This commit updates the installation instructions to reflect that Copilot is
compatible with versions of GHC 9.10 as of this writing.

Author: estherdconrad

copilot/README.md

@@ -100,7 +100,7 @@ ghci> ghci> Leaving GHCi.
 On other Linux distributions or older Debian-based distributions, to use
 Copilot you must install a Haskell compiler (GHC) and the package manager
 Cabal. We currently support all versions of GHC from 8.6.5 to modern versions
-(9.8 as of this writing). You can install the toolchain using
+(9.10 as of this writing). You can install the toolchain using
 [ghcup](https://www.haskell.org/ghcup/) or, if you are on Debian/Ubuntu,
 you can use `apt-get` to install all dependencies as follows: