create index use txn_merge instead of ingest due to not enough storage capacity of TiFlash

[shuke987]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. deploy a cluster with TiFlash nodes, and make TiFlash nodes with no more than 10% storage capacity left.
2. create index

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

use ingest when create index

3. What did you see instead (Required)

change to txn merge.
The reason maybe TiFlash peers are not excluded when local checking.

tidb/br/pkg/lightning/backend/local/local.go

Line 909 in c30a9ff

for _, peer := range region.Region.GetPeers() {

4. What is your TiDB version? (Required)

v6.5.0