Fix bug where schedules without a slug or active raise a 500

[desertaxle]

This PR ensures that we default to active=True when schedules are recreated via a call to the POST /deployments endpoint. This preserves the behavior exhibited prior to the introduction of deployment schedule slugs.

[codspeed-hq]

CodSpeed Performance Report

Merging #17091 will not alter performance

_{Comparing fix-create-deployment-on-update-no--slug (c086bbb) with main (3c5112d)}

Summary

✅ 2 untouched benchmarks