haskell.packages.ghcHEAD: mv configuration-ghc-{head,9.8.x}.nix

GHC HEAD is a pre basically pre GHC 9.8 (or rather 9.7 something).
Let's name the configuration like the upcoming release, so we can use it
immediately when the new release comes out. Instead of keeping the HEAD
configuration like we used to, we'd create a new (empty) one.

pkgs/top-level/haskell-packages.nix

@@ -406,7 +406,7 @@ in {
     ghcHEAD = callPackage ../development/haskell-modules {
       buildHaskellPackages = bh.packages.ghcHEAD;
       ghc = bh.compiler.ghcHEAD;
-      compilerConfig = callPackage ../development/haskell-modules/configuration-ghc-head.nix { };
+      compilerConfig = callPackage ../development/haskell-modules/configuration-ghc-9.8.x.nix { };
     };
 
     ghcjs = packages.ghcjs810;