Fix typo in the outputs variable (#4558)

So, the Slack notifications are sent when a versions file update is created.

Author: rdner

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

@@ -31,5 +31,6 @@ else
        --label 'skip-changelog' \
        --label 'backport-skip' \
        --repo $GITHUB_REPOSITORY)
-    echo "pr=$pr" >> $GITHUB_OUTPUT # set the step output for Slack notifications
+    echo "pr=$pr" >> "$GITHUB_OUTPUT" # set the step output for Slack notifications
+    echo "Created a PR with the file update: $pr"
 fi

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

@@ -55,7 +55,7 @@ jobs:
           channel: "#ingest-notifications"
 
         # if a PR was created as a result of this job, we notify on the Slack channel
-      - if: ${{ startsWith(steps.update.output.pr, 'https') }}
+      - if: ${{ startsWith(steps.update.outputs.pr, 'https') }}
         uses: elastic/apm-pipeline-library/.github/actions/slack-message@current
         with:
           url: ${{ secrets.VAULT_ADDR }}