ci: update action-download-artifact to v6

Agent-Logs-Url: https://github.com/fsprojects/FSharp.Data.GraphQL/sessions/ae314b8b-9c8a-4f87-a8b0-b77c4bfa2cef

Co-authored-by: xperiandri <2365592+xperiandri@users.noreply.github.com>

Author: Copilot

.github/workflows/publish-test-results.yml

@@ -21,14 +21,14 @@ jobs:
 
     steps:
     - name: Download event file
-      uses: dawidd6/action-download-artifact@v4
+      uses: dawidd6/action-download-artifact@v6
       with:
         run_id: ${{ github.event.workflow_run.id }}
         path: artifacts
         name: EventFile
 
     - name: Download test results
-      uses: dawidd6/action-download-artifact@v4
+      uses: dawidd6/action-download-artifact@v6
       with:
         run_id: ${{ github.event.workflow_run.id }}
         path: test-results