tikv rpc request source tag unset

[crazycs520]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

introduce by #47745

    session_test.go:780: 
        	Error Trace:	pkg/session/test/session_test.go:780
        	            				external/com_github_tikv_client_go_v2/internal/client/client_interceptor.go:125
        	            				external/com_github_tikv_client_go_v2/internal/client/client_interceptor.go:60
        	            				external/com_github_tikv_client_go_v2/internal/client/client_collapse.go:74
        	            				external/com_github_tikv_client_go_v2/internal/locate/region_request.go:1681
        	            				external/com_github_tikv_client_go_v2/internal/locate/region_request.go:1461
        	            				external/com_github_tikv_client_go_v2/txnkv/txnsnapshot/client_helper.go:146
        	            				external/com_github_tikv_client_go_v2/txnkv/txnsnapshot/snapshot.go:682
        	            				external/com_github_tikv_client_go_v2/txnkv/txnsnapshot/snapshot.go:580
        	            				pkg/store/driver/txn/snapshot.go:60
        	            				pkg/executor/point_get.go:493
        	            				pkg/executor/point_get.go:373
        	            				pkg/executor/point_get.go:310
        	            				pkg/executor/internal/exec/executor.go:283
        	            				pkg/executor/adapter.go:1222
        	            				pkg/executor/adapter.go:154
        	            				pkg/session/tidb.go:350
        	            				pkg/session/tidb.go:368
        	            				pkg/testkit/testkit.go:251
        	            				pkg/testkit/testkit.go:177
        	            				pkg/session/test/session_test.go:794
        	Error:      	Not equal: 
        	            	expected: "leader_external_Select_lightning"
        	            	actual  : ""
        	            	
        	            	Diff:
        	            	--- Expected
        	            	+++ Actual
        	            	@@ -1 +1 @@
        	            	-leader_external_Select_lightning
        	            	+
        	Test:       	TestRequestSource

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your TiDB version? (Required)

[crazycs520]

release-7.5 already fix this issue.