receipt: dequeue not returning watch err

[wxsms]

the error from watch is not returned, if the client token expired, the ev return by watch will be nil, therefore the Deque method will panic in such case.

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

Hi @wxsms. Thanks for your PR.

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[serathius]

Can you add a test?

[wxsms]

Hi there, Thanks for reply, I just added a test to simulate an error during watch by shutting down a cluster, since I'm very new to etcd, not sure if I make it correctly. The main propose of this PR is to make sure watch return a non-nil value or error. The testcase will failed as followed if queue code stay untouched:

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x8 pc=0xad0bb6]

goroutine 169 [running]:
go.etcd.io/etcd/client/v3/experimental/recipes.(*Queue).Dequeue(0xc00045b290)
        /workspaces/etcd/client/v3/experimental/recipes/queue.go:70 +0x1f6
go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes_test.TestQueueWatchError.func1()
        /workspaces/etcd/tests/integration/clientv3/experimental/recipes/v3_queue_test.go:92 +0x25
created by go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes_test.TestQueueWatchError in goroutine 64
        /workspaces/etcd/tests/integration/clientv3/experimental/recipes/v3_queue_test.go:91 +0x153
FAIL    go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes      1.107s

[wxsms]

Sry but I have no idea why integration/clientv3 TestMaintenanceSnapshotCancel failing, every thing's fine while running tests inside my codespace, including this one. Can anyone help to take a look?

[jmhbnz]

/retest

[serathius]

/retest

[siyuanfoundation]

cc @moficodes

[serathius]

/retest