"Suppress automatic SCM triggering" property must be respected when events trigger the build

Steps to reproduce:

1. Create multibranch pipeline project.
2. Under project configuration, add GitHub source.
3. Select "All branches get the same properties" under Property Strategy.
4. Add "Suppress automatic SCM triggering" property.
5. Save configuration.
6. Make sure that GitHub repo configured at step 2 sends push notifications to your Jenkins instance via /github-webhook endpoint.
7. Push something to the repo.

Expected result

Build triggering was suppressed.

Actual result

Build is triggered.

This got broken after recent 1.x -> 2.x updates to SCM API and Co.