TestAllocID is flaky

[okJiang]

Flaky Test

Which jobs are failing

    server_test.go:98: 
        	Error Trace:	/home/runner/work/pd/pd/tests/integrations/mcs/scheduling/server_test.go:98
        	Error:      	Received unexpected error:
        	            	API server leader is not found
        	            	github.com/tikv/pd/pkg/mcs/scheduling/server.(*Cluster).getAPIServerLeaderClient
        	            		/home/runner/work/pd/pd/pkg/mcs/scheduling/server/cluster.go:243
        	            	github.com/tikv/pd/pkg/mcs/scheduling/server.(*Cluster).AllocID
        	            		/home/runner/work/pd/pd/pkg/mcs/scheduling/server/cluster.go:225
        	            	github.com/tikv/pd/tests/integrations/mcs/scheduling.(*serverTestSuite).TestAllocID
        	            		/home/runner/work/pd/pd/tests/integrations/mcs/scheduling/server_test.go:97
        	            	reflect.Value.call
        	            		/opt/hostedtoolcache/go/1.23.2/x64/src/reflect/value.go:581
        	            	reflect.Value.Call
        	            		/opt/hostedtoolcache/go/1.23.2/x64/src/reflect/value.go:365
        	            	github.com/stretchr/testify/suite.Run.func1
        	            		/home/runner/go/pkg/mod/github.com/stretchr/testify@v1.9.0/suite/suite.go:202
        	            	testing.tRunner
        	            		/opt/hostedtoolcache/go/1.23.2/x64/src/testing/testing.go:1690
        	            	runtime.goexit
        	            		/opt/hostedtoolcache/go/1.23.2/x64/src/runtime/asm_amd64.s:1700
        	Test:       	TestServerTestSuite/TestAllocID

CI link

https://github.com/tikv/pd/actions/runs/11323255302/job/31487695893?pr=8699

Reason for failure (if possible)

Anything else