gha: set-output was deprecated

Author: coot

.github/workflows/haskell.yml

@@ -66,7 +66,7 @@ jobs:
       run: |
         cabal build all --dry-run
         cat dist-newstyle/cache/plan.json | jq -r '."install-plan"[].id' | sort | uniq > dependencies.txt
-        echo "::set-output name=weeknum::$(/bin/date -u "+%W")"
+        echo "weeknum=$(/bin/date -u "+%W")" >> $GITHUB_OUTPUT
 
     - uses: actions/cache@v3
       name: "Cache cabal store"