memory leak of evicted stmt summary

[tiancaiamao]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

The same script with #56619

After creating 2M users, change the script to "alter user ..." to update password for 2M users.

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

No memory leak

3. What did you see instead (Required)

Take the heap profile after a while:

And after a long time later:

As you can see, the statement summary increase dramatically, this indicate a memory leak!

The test script execute 'alter user test%d ...' for 2M times, and the leaked object count is almost 2M:

4. What is your TiDB version? (Required)

master

[tiancaiamao]

Introduced by #24513