ci: building with oldest ghc is enough, save some carbon

Author: simonmichael

.github/workflows/ci.yml

@@ -37,8 +37,7 @@ jobs:
       matrix:
         plan:
         - { ghc: "810" , stackyaml: "stack8.10.yaml", stack: "stack --stack-yaml=stack8.10.yaml" }
-        - { ghc: "94"  , stackyaml: "stack9.4.yaml", stack: "stack --stack-yaml=stack9.4.yaml" }
-        - { ghc: "96"  , stackyaml: "stack.yaml", stack: "stack --stack-yaml=stack.yaml" }
+        # - { ghc: "96"  , stackyaml: "stack.yaml", stack: "stack --stack-yaml=stack.yaml" }
 
     steps: