AlterResourceGroup does not retry when internal RPC encounters temporary service unavailable

## Bug Report

Please answer these questions before submitting your issue. Thanks!

### 1. Minimal reproduce step (Required)

We set up the TiDB following the [quick start in Kubernetes](https://docs.pingcap.com/tidb-in-kubernetes/stable/get-started) and then executed the SQL below.

```sql
CREATE RESOURCE GROUP rg1 RU_PER_SEC = 100;
ALTER RESOURCE GROUP rg1 RU_PER_SEC = 200;
```

When executing AlterResourceGroup, RPC `ModifyResourceGroup` encountered temporary service unavailable and then failed the statement without retry.

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

AlterResourceGroup retries the RPC `ModifyResourceGroup` when encountering temporary service unavailable, like CreateResourceGroup retries RPC `AddResourceGroup`.

### 3. What did you see instead (Required)

When RPC `ModifyResourceGroup` encountered temporary service unavailable, it failed the statement without retry.

### 4. What is your TiDB version? (Required)

```
Release Version: v8.5.0
Edition: Community
Git Commit Hash:
Git Branch: master
UTC Build Time: 2025-03-19 08:15:18
GoVersion: go1.23.7
Race Enabled: false
Check Table Before Drop: true
Store: tikv
```