CI: Avoid potential template injection issue in create-upload-suggestions

Solves zizmor's template-injection audit: https://docs.zizmor.sh/audits/#template-injection

Author: echoix

.github/actions/create-upload-suggestions/action.yml

@@ -145,7 +145,9 @@ runs:
     - name: List all changed files tracked and untracked files
       shell: bash
       run: |
-        echo "Changed files: ${{ steps.git-changed-files.outputs.CHANGED_FILES }}"
+        echo "Changed files: ${CHANGED_FILES}"
+      env:
+        CHANGED_FILES: ${{ steps.git-changed-files.outputs.CHANGED_FILES }}
     - name: Add job summary without changed files
       shell: bash
       if: ${{ steps.files_changed.outputs.files_changed == 'false' }}