Post a link to a created PR on Slack when versions file is updated (#4554)

Also, use the new / non-depricated approach to outputs.

Author: rdner

.github/workflows/bump-agent-versions.sh

@@ -22,14 +22,14 @@ else
 
     git commit -m "[$GITHUB_REF_NAME][Automation] Update .agent-versions.json" -m "$commit_desc"
     git push --set-upstream origin "update-agent-versions-$GITHUB_RUN_ID"
-    gh pr create \
+    pr=$(gh pr create \
        --base "$GITHUB_REF_NAME" \
        --fill-first \
        --head "update-agent-versions-$GITHUB_RUN_ID" \
        --label 'Team:Elastic-Agent' \
        --label 'update-versions' \
        --label 'skip-changelog' \
        --label 'backport-skip' \
-       --repo $GITHUB_REPOSITORY
-    echo "::set-output name=pr::true" # set step output for notifications
+       --repo $GITHUB_REPOSITORY)
+    echo "pr=$pr" >> $GITHUB_OUTPUT # set the step output for Slack notifications
 fi

.github/workflows/bump-agent-versions.yml

@@ -54,11 +54,12 @@ jobs:
           message: ":traffic_cone: Elastic Agent versions file update failed: ${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}"
           channel: "#ingest-notifications"
 
-      - if: ${{ success() && steps.update.output.pr == true}}
+        # if a PR was created as a result of this job, we notify on the Slack channel
+      - if: ${{ startsWith(steps.update.output.pr, 'https') }}
         uses: elastic/apm-pipeline-library/.github/actions/slack-message@current
         with:
           url: ${{ secrets.VAULT_ADDR }}
           roleId: ${{ secrets.VAULT_ROLE_ID }}
           secretId: ${{ secrets.VAULT_SECRET_ID }}
-          message: "Update for Elastic Agent versions file has been created https://github.com/elastic/elastic-agent/pulls?q=is%3Aopen+is%3Apr+label%3Aupdate-versions"
+          message: "Update for Elastic Agent versions file has been created: ${{ steps.update.output.pr }}"
           channel: "#ingest-notifications"