GH Actions: fix use of deprecated `set-output` (#11126)

GitHub has deprecated the use of `set-output` (and `set-state`) in favour of new environment files.

This commit updates workflows to use the new methodology.

Refs:
* https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
* https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#environment-files

Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>

.github/workflows/phpstan.yml

@@ -45,7 +45,7 @@ jobs:
 
       - name: "Determine composer cache directory"
         id: "determine-composer-cache-directory"
-        run: "echo \"::set-output name=directory::$(composer config cache-dir)\""
+        run: "echo \"directory=$(composer config cache-dir)\" >> $GITHUB_OUTPUT"
 
       - name: "Cache dependencies installed with composer"
         uses: "actions/cache@v3"