Panic in TestWatchEvent

[gibmat]

TestWatchEvent seems to fail randomly, but with a high failure rate. It may be easier to reproduce on a slower machine. Seen in both gobgp 3.29.0 and 3.30.0.

=== RUN   TestWatchEvent
time="2024-10-27T05:43:51Z" level=info msg="Add a peer configuration" Key=127.0.0.1 Topic=Peer
time="2024-10-27T05:43:51Z" level=info msg="Add a peer configuration" Key=127.0.0.1 Topic=Peer
time="2024-10-27T05:44:00Z" level=info msg="Peer Up" Key=127.0.0.1 State=BGP_FSM_OPENCONFIRM Topic=Peer
time="2024-10-27T05:44:00Z" level=info msg="Peer Up" Key=127.0.0.1 State=BGP_FSM_OPENCONFIRM Topic=Peer
time="2024-10-27T05:44:00Z" level=info msg="Delete a peer configuration" Key=127.0.0.1 Topic=Peer
time="2024-10-27T05:44:00Z" level=info msg="Peer Down" Key=127.0.0.1 Reason=dying State=BGP_FSM_ESTABLISHED Topic=Peer
time="2024-10-27T05:44:00Z" level=info msg="Delete a peer configuration" Key=127.0.0.1 Topic=Peer
panic: close of closed channel

goroutine 511 [running]:
github.com/osrg/gobgp/pkg/server.TestWatchEvent.func1(0x4791e9?)
	/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/src/github.com/osrg/gobgp/pkg/server/server_test.go:2328 +0x4e
github.com/osrg/gobgp/pkg/server.(*BgpServer).WatchEvent.func1({0x13ee420, 0x0, 0x0})
	/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/src/github.com/osrg/gobgp/pkg/server/server.go:4263 +0xd4
github.com/osrg/gobgp/pkg/server.(*BgpServer).WatchEvent.func2()
	/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/src/github.com/osrg/gobgp/pkg/server/server.go:4284 +0x7ef
created by github.com/osrg/gobgp/pkg/server.(*BgpServer).WatchEvent in goroutine 464
	/<<PKGBUILDDIR>>/obj-x86_64-linux-gnu/src/github.com/osrg/gobgp/pkg/server/server.go:4266 +0x2f1
FAIL	github.com/osrg/gobgp/pkg/server	103.339s

(Forwarded from Debian bug #1078512; additional logs available at https://people.debian.org/~sanvila/build-logs/gobgp/)