[Ops] Fix indentation issue in on_merge.yml

[delanni]

Summary

Fix indentation issue introduced in #171868 - I missed it in the review

[delanni]

Closing because the issue was reverted

[kibana-ci]

💔 Build Failed

• Buildkite Build
• Commit: 0b6d8c3
• Interpreting CI Failures

Failed CI Steps

• Investigations - Security Solution Cypress Tests #3
• Investigations - Security Solution Cypress Tests #5
• Post-Build

Test Failures

• [job] [logs] Investigations - Security Solution Cypress Tests #5 / Save Timeline Prompts "before each" hook for "Changed & saved timeline should NOT prompt when user navigates within security solution where timelines are disabled" "before each" hook for "Changed & saved timeline should NOT prompt when user navigates within security solution where timelines are disabled"
• [job] [logs] Investigations - Security Solution Cypress Tests #3 / Timelines shows the different timeline states "before all" hook for "should show the correct timeline status" "before all" hook for "should show the correct timeline status"

Metrics [docs]

‼️ ERROR: no builds found for mergeBase sha [36c86fc]

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream