try to get pull request id from github.event.workflow_run.pull_requests

.github/workflows/report-api-diff.yml

@@ -39,7 +39,14 @@ jobs:
         run: unzip api-artifact.zip -d artifacts
       - name: Load PR Number
         id: load-pr-num
-        run: echo "pr-number=$(cat artifacts/pr_number)" >> "$GITHUB_OUTPUT"
+        env:
+          PULL_REQUESTS: ${{ toJson(github.event.workflow_run.pull_requests.*) }}
+          REPO_ID: ${{ github.repository_id }}
+        run: |
+          # find first pull requests that targets this repository
+          PR_NUMBER="$(echo "$PULL_REQUESTS"
+              | jq --arg REPO_ID "$REPO_ID" '[.[] | select ($REPO_ID == (.base.repo.id | tostring)) | .id ][0]')"
+          echo "pr-number=$PR_NUMBER" >> "$GITHUB_OUTPUT"
 
       - name: Output base
         run: cat ./artifacts/api-base.json