Benjamin Wang 3c51c42417 test: fix nil pointer panic in testMutexLock
Refer to: https://github.com/etcd-io/etcd/actions/runs/3671847902/jobs/6207463700

```
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xedc388]

goroutine 5253 [running]:
go.etcd.io/etcd/client/v3/concurrency.(*Session).Client(...)
	/home/runner/work/etcd/etcd/client/v3/concurrency/session.go:76
go.etcd.io/etcd/client/v3/concurrency.(*Mutex).tryAcquire(0xc000133140, {0x18a8668, 0xc000050158})
	/home/runner/work/etcd/etcd/client/v3/concurrency/mutex.go:111 +0x88
go.etcd.io/etcd/client/v3/concurrency.(*Mutex).Lock(0xc000133140, {0x18a8668, 0xc000050158})
	/home/runner/work/etcd/etcd/client/v3/concurrency/mutex.go:74 +0x68
go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes_test.testMutexLock.func1()
	/home/runner/work/etcd/etcd/tests/integration/clientv3/experimental/recipes/v3_lock_test.go:65 +0x285
created by go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes_test.testMutexLock
	/home/runner/work/etcd/etcd/tests/integration/clientv3/experimental/recipes/v3_lock_test.go:59 +0xda
FAIL	go.etcd.io/etcd/tests/v3/integration/clientv3/experimental/recipes	7.070s
FAIL
```

Signed-off-by: Benjamin Wang <wachao@vmware.com>
2022-12-12 10:18:45 +08:00
..
2022-12-09 07:39:57 +08:00
2022-12-09 07:39:57 +08:00
2022-02-08 05:41:21 +08:00
2022-12-09 08:54:48 +08:00
2022-12-09 08:54:48 +08:00