Expired WATCH resource group settings should no longer take effect

[JmPotato]

Bug Report

1. Minimal reproduce step (Required)

Let's assume at T1 we have a resource group rg1 with QUERY_LIMIT like:

ALTER RESOURCE GROUP rg1 QUERY_LIMIT=(EXEC_ELAPSED='60s', ACTION=KILL, WATCH=SIMILAR DURATION='10m');

We change this resource group at T2 to:

ALTER RESOURCE GROUP rg1 QUERY_LIMIT=(RU = 1000, ACTION=SWITCH_GROUP(default), WATCH=SIMILAR DURATION='10m');

Then, a SQL query that starts between T1 and T2 reaches its previous EXEC_ELAPSED threshold at T3, triggering a watch rule that uses the expired QUERY_LIMIT settings to be added.

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

Once the QUERY_LIMIT settings are changed after T2, the old watch rule should not take effect any more.

3. What did you see instead (Required)

After T3, both types of rules will be triggered within a maximum of 10 minutes.

4. What is your TiDB version? (Required)

56ba961