Work around hls hackage constraint issue (#1043)

Author: hamishmack

overlays/hackage-quirks.nix

@@ -66,8 +66,12 @@ in { haskell-nix = prev.haskell-nix // {
     };
 
     haskell-language-server = {
-      # Pin for now as current hackage is broken
-      index-state = "2021-02-08T00:00:00Z";
+      cabalProject = ''
+        packages: .
+        allow-newer: haskell-language-server:ghcide
+        constraints: ghcide <0.7.4
+      '';
+      configureArgs = "--disable-benchmarks --disable-tests";
     };
 
   }."${name}" or {};