copilot: Update README to reflect support for GHC 9.8. Refs #518.

A recent update to copilot-language makes all of Copilot compatible with
GHC 9.8. This commit updates the README to reflect such compatibility.

Author: ivanperez-keera

copilot/README.md

@@ -81,7 +81,7 @@ 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
-(9.6 as of this writing). You can install the toolchain using
+(9.8 as of this writing). You can install the toolchain using
 [ghcup](https://www.haskell.org/ghcup/) or, if you are on Debian/Ubuntu,
 directly with `apt-get`: