Simplify and update CI scripts

.gitlab-ci.yml

@@ -8,11 +8,13 @@ ci:
   tags:
     - x86_64-linux
   script:
+    - nix-env -iA cachix -f https://cachix.org/api/v1/install
+    - cachix use ghc
     - nix-shell -p git
-    - nix-shell
+    - nix-env -f shell.nix -i -A 'buildInputs'
     - cabal update
-    - cabal build debugger
-    - cabal test
+    - cabal build -w ghc-9.2.4 ghc-debug-brick ghc-debug-common ghc-debug-convention ghc-debug-client ghc-debug-stub
+    - cabal test -w ghc-9.2.4
 
 pages:
   script: