[github] arm "cabal check" workflow

Author: mauke

.github/workflows/haskell.yml

@@ -78,9 +78,12 @@ jobs:
     - name: check
       shell: bash
       run: |
+        ok=x
         for i in */*.cabal; do
-          ( cd "${i%/*}" && cabal check ) || break
+          ( cd "${i%/*}" && echo "[${i%/*}]" && cabal check ) || ok=
         done
+        echo "[ok=$ok]"
+        [ "$ok" ] || exit 1
 
     - name: documentation
       run: cabal haddock all