NotifyUpdateSysVarCache misses a timeout deadline on etcd request

[qts0312]

Bug Report

Function NotifyUpdateSysVarCache in pkg/domain/domain.go does not set a timeout deadline for etcd request Put

_, err := row.Put(context.Background(), sysVarCacheKey, "")

As the background context will never be canceled, this function will stuck endlessly when the etcd request meets a timeout error.

1. Minimal reproduce step (Required)

Any statements related to NotifyUpdateSysVarCache, for example

set global tidb_enable_check_constraint=ON;

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

row.Put(context.Background(), sysVarCacheKey, "") returns DeadlineExceeded.

3. What did you see instead (Required)

row.Put(context.Background(), sysVarCacheKey, "") is stuck, and further block NotifyUpdateSysVarCache endlessly.

4. What is your TiDB version? (Required)

v8.5.0

[qts0312]

fixed by PR #61154