flaky test TestParallelErrStage

[hawkingrei]

Bug Report

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1. Minimal reproduce step (Required)

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

3. What did you see instead (Required)

     scheduler_test.go:207: 
        	Error Trace:	pkg/disttask/framework/scheduler/scheduler_test.go:207
        	            				pkg/disttask/framework/scheduler/scheduler_test.go:226
        	            				pkg/disttask/framework/scheduler/scheduler_test.go:351
        	Error:      	Not equal: 
        	            	expected: 2
        	            	actual  : 30001
        	Test:       	TestParallelErrStage 

4. What is your TiDB version? (Required)

[hawkingrei]

https://tiprow.hawkingrei.com/view/gs/pingcapprow/pr-logs/pull/pingcap_tidb/55592/fast_test_tiprow/1826537425518727168#1:build-log.txt%3A2469

[tangenta]

When full schema reload happens, the auto ID will jump because the allocators are reconstructed. #55229 enables schema cache by default and makes each testkit session switches to v1 with 30% probability. When the schema is reload, it must be a full reload.

As a result, the auto ID jump is expected.