tests: panic in tso test

[lhy1024]

Flaky Test

Which jobs are failing

2023-11-23T14:29:54.8804918Z panic: runtime error: invalid memory address or nil pointer dereference
2023-11-23T14:29:54.8805393Z [signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0x199ed19]
2023-11-23T14:29:54.8805408Z 
2023-11-23T14:29:54.8805572Z goroutine 192514 [running]:
2023-11-23T14:29:54.8805862Z github.com/tikv/pd/pkg/member.(*Participant).IsLeader(0xc0019419e0)
2023-11-23T14:29:54.8806271Z 	/home/runner/work/pd/pd/pkg/member/participant.go:127 +0xb9
2023-11-23T14:29:54.8806572Z github.com/tikv/pd/pkg/tso.waitForPrimariesServing.func1()
2023-11-23T14:29:54.8806908Z 	/home/runner/work/pd/pd/pkg/tso/keyspace_group_manager_test.go:1229 +0x115
2023-11-23T14:29:54.8807101Z github.com/stretchr/testify/assert.Eventually.func1()
2023-11-23T14:29:54.8807520Z 	/home/runner/go/pkg/mod/github.com/stretchr/testify@v1.8.2/assert/assertions.go:1737 +0x34
2023-11-23T14:29:54.8807827Z created by github.com/stretchr/testify/assert.Eventually in goroutine 66646
2023-11-23T14:29:54.8808233Z 	/home/runner/go/pkg/mod/github.com/stretchr/testify@v1.8.2/assert/assertions.go:1737 +0x376
2023-11-23T14:29:54.8808381Z FAIL	github.com/tikv/pd/pkg/tso	22.148s

https://github.com/lhy1024/pd/actions/runs/6971008658/job/18970106131?pr=27

CI link

Reason for failure (if possible)

Anything else