Upgrade dawidd6/action-download-artifact to v20 and filter by name

Automattic/jetpack#47415 upgraded to actions/upload-artifact@v7, which
introduced archive: false for build cache artifacts. dawidd6 v11 could
not handle the mix of zipped and non-zipped artifacts when downloading
all artifacts from a run.

Upgrade to v20 (which uses @actions/artifact@6.2.1) and add a name
filter (test-output-*) to only download the test output artifacts the
report generation needs.

Also fix workflow_dispatch payload handling so the workflow can be
triggered manually for testing.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: Mahangu Weerasinghe

.github/workflows/report.yml

@@ -33,7 +33,7 @@ jobs:
 
       - name: Set environment variables safely
         env:
-          PAYLOAD: ${{ toJson(github.event.client_payload) }}
+          PAYLOAD: ${{ github.event.inputs.client_payload || toJson(github.event.client_payload) }}
         run: |
           # Use jq to safely extract values from client_payload
           echo "PR_NUMBER=$(echo "$PAYLOAD" | jq -r '.pr_number // ""')" >> $GITHUB_ENV
@@ -82,12 +82,14 @@ jobs:
         run: ./bin/wait-for-artifacts.sh
 
       - name: Download artifacts
-        uses: dawidd6/action-download-artifact@23e7b2e9aa32a408a649c4fca36dee127ff5d325 # v11
+        uses: dawidd6/action-download-artifact@v20
         with:
           repo: Automattic/jetpack
           workflow: e2e-tests.yml
           workflow_conclusion: "completed"
           run_id: ${{ env.RUN_ID }}
+          name: test-output-*
+          name_is_regexp: true
           path: ../downloads
 
       - name: Generate test report