fix: don't use deprecated set-output in github actions

Author: joostdebruijn

.github/workflows/tests.yml

@@ -38,7 +38,7 @@ jobs:
       - name: Get Composer cache directory
         id: composer-cache
         run: |
-          echo "::set-output name=dir::$(composer config cache-files-dir)"
+          echo "dir=$(composer config cache-files-dir)" >> $GITHUB_OUTPUT
 
       - uses: actions/cache@v4
         with: