Make default markdown height `3`

[JCZuurmond]

More consistent with tho other tiles

[github-actions[bot]]

✅ 31/31 passed, 1 flaky, 2 skipped, 10m48s total

Flaky tests:

• 🤪 test_dashboard_deploys_dashboard_the_same_as_created_dashboard (9.012s)

_{Running from acceptance #211}