forbid older Cabal libs

Author: ulysses4ever

.github/workflows/validate.yml

@@ -115,6 +115,7 @@ jobs:
       - name: Allow newer boot libraries
         run: |
           echo "allow-newer: base, template-haskell, ghc-prim" >> cabal.project.validate
+          echo "constraints: Cabal-syntax 3.9.0.0" >> cabal.project.validate
 
       - name: Set validate inputs
         run: |