While some builds are succeeding, three recent builds:

https://github.com/syncthing/syncthing/actions/runs/5777466439/job/15660650363#step:7:1738 (Go 1.19, but not 1.20)
https://github.com/syncthing/syncthing/actions/runs/5778159436/job/15659077804#step:7:1798 (Go 1.19, but not 1.20)
https://github.com/syncthing/syncthing/actions/runs/5780780108/job/15664908391#step:7:1742 (Go 1.20, but not 1.19)

all panicked with

panic: bug: ClusterConfig called on closed or nonexistent connection

This panic is emitted at lib/model/model.go:1176.

It may be related to #9007 which touched the code near this panic call.