tidb_enable_gc_aware_memory_track is not disabled when upgraded from versions from 6.2 to 6.4

[chrysan]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. create a v6.2/v6.3/v6.4 cluster
2. upgrade to v6.5
3. select @@tidb_enable_gc_aware_memory_track;

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

tidb_enable_gc_aware_memory_track is OFF.

3. What did you see instead (Required)

tidb_enable_gc_aware_memory_track is ON.

4. What is your TiDB version? (Required)

v6.5