GH Actions: fix use of deprecated set-output

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

.github/workflows/quicktest.yml

@@ -50,9 +50,9 @@ jobs:
         id: set_ini
         run: |
           if [ "${{ matrix.phpcs_version }}" != "dev-master" ]; then
-            echo '::set-output name=PHP_INI::error_reporting=E_ALL & ~E_DEPRECATED, display_errors=On'
+            echo 'PHP_INI=error_reporting=E_ALL & ~E_DEPRECATED, display_errors=On' >> $GITHUB_OUTPUT
           else
-            echo '::set-output name=PHP_INI::error_reporting=-1, display_errors=On'
+            echo 'PHP_INI=error_reporting=-1, display_errors=On' >> $GITHUB_OUTPUT
           fi
 
       - name: Set up PHP

.github/workflows/unit-tests.yml

@@ -56,9 +56,9 @@ jobs:
         id: set_ini
         run: |
           if [ "${{ matrix.phpcs_version }}" != "dev-master" ]; then
-            echo '::set-output name=PHP_INI::error_reporting=E_ALL & ~E_DEPRECATED, display_errors=On'
+            echo 'PHP_INI=error_reporting=E_ALL & ~E_DEPRECATED, display_errors=On' >> $GITHUB_OUTPUT
           else
-            echo '::set-output name=PHP_INI::error_reporting=-1, display_errors=On'
+            echo 'PHP_INI=error_reporting=-1, display_errors=On' >> $GITHUB_OUTPUT
           fi
 
       - name: Set up PHP