Occasional CI timing out

[merlinran]

It looks like the semaphore was kept being hold by some other goroutine? what caused the panic is interesting too.

2021-06-29T22:04:08.9913038Z goroutine 37 [chan send, 9 minutes]:
2021-06-29T22:04:08.9914108Z github.com/textileio/go-threads/net/util.(*Semaphore).Acquire(...)
2021-06-29T22:04:08.9915151Z 	/home/runner/work/go-threads/go-threads/net/util/util.go:38
2021-06-29T22:04:08.9916358Z github.com/textileio/go-threads/net/util.(*SemaphorePool).Stop(0xc000270580)
2021-06-29T22:04:08.9917476Z 	/home/runner/work/go-threads/go-threads/net/util/util.go:96 +0x165
2021-06-29T22:04:08.9918619Z github.com/textileio/go-threads/net.(*net).Close(0xc0001f6180, 0x0, 0x0)
2021-06-29T22:04:08.9919847Z 	/home/runner/work/go-threads/go-threads/net/net.go:258 +0x7c
2021-06-29T22:04:08.9920406Z panic(0x16310c0, 0x245cc20)
2021-06-29T22:04:08.9921343Z 	/opt/hostedtoolcache/go/1.15.13/x64/src/runtime/panic.go:975 +0x47a
2021-06-29T22:04:08.9922496Z github.com/libp2p/go-libp2p-pubsub.(*Subscription).Cancel(0x0)
2021-06-29T22:04:08.9923861Z 	/home/runner/go/pkg/mod/github.com/libp2p/go-libp2p-pubsub@v0.4.0/subscription.go:40 +0x4d
2021-06-29T22:04:08.9925265Z github.com/textileio/go-threads/net.(*PubSub).Remove(0xc0007af4a0, 0xc0007d6510, 0x22, 0x0, 0x0)
2021-06-29T22:04:08.9926384Z 	/home/runner/work/go-threads/go-threads/net/pubsub.go:93 +0x15a
2021-06-29T22:04:08.9927810Z github.com/textileio/go-threads/net.(*net).deleteThread(0xc0001f6180, 0x1b3f0a0, 0xc000120010, 0xc0007d6510, 0x22, 0x1, 0x1)
2021-06-29T22:04:08.9929049Z 	/home/runner/work/go-threads/go-threads/net/net.go:547 +0x467
2021-06-29T22:04:08.9930497Z github.com/textileio/go-threads/net.(*net).DeleteThread(0xc0001f6180, 0x1b3f0a0, 0xc000120010, 0xc0007d6510, 0x22, 0x0, 0x0, 0x0, 0x0, 0x0)
2021-06-29T22:04:08.9931681Z 	/home/runner/work/go-threads/go-threads/net/net.go:533 +0x49b
2021-06-29T22:04:08.9932881Z github.com/textileio/go-threads/net.TestNet_DeleteThread(0xc000012180)
2021-06-29T22:04:08.9934109Z 	/home/runner/work/go-threads/go-threads/net/net_test.go:404 +0x62f

Full log can be seen from logs_949.zip