br v6.0.0-nightly backup/restore v5.4.0 failed due to major version mismatch

[fubinzh]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

1. Use v6.0.0-nightly to backup tidb cluster v5.4.0
2. Use v6.0.0-nightly to restore to tidb cluster v5.4.0

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

Backup and restore should be successful per compatibility requirements

3. What did you see instead (Required)

Backup & restore failed due to major version mismatch (note: backup & restore can be successful if specifying --check-requirements=false.

/br  backup  db "-s" "s3://tmp/br-backup-basic802f9500-b4a1-4d00-ac92-09247420bc57?access-key=minioadmin&secret-access-key=minioadmin&endpoint=http%3a%2f%2fminio.pingcap.net%3a9000&force-path-style=true" "-u" "http://upstream-pd.brie-acceptance-compatiblity-tps-606274-1-710:2379" "--db" "clustered"
[2022/03/05 04:48:16.700 +00:00] [INFO] [collector.go:67] ["Database backup failed summary"] [total-ranges=0] [ranges-succeed=0] [ranges-failed=0]
Error: running BR in incompatible version of cluster, if you believe it's OK, use --check-requirements=false to skip.: TiKV node upstream-tikv-2.upstream-tikv-peer.brie-acceptance-compatiblity-tps-606274-1-710.svc:20160 version 5.4.0 and BR v6.0.0-nightly major version mismatch, please use the same version of BR: [BR:Common:ErrVersionMismatch]version mismatch

/br  restore db "-s" "s3://tmp/br-backup-basic2c276983-3ad4-4be0-9c66-24cc1a31ff04?access-key=minioadmin&secret-access-key=minioadmin&endpoint=http%3a%2f%2fminio.pingcap.net%3a9000&force-path-style=true" "-u" "http://dst-tidb-pd.fb-testbed-comp-rlj79:2379" "--db" "clustered"
Detail BR log in /tmp/br.log.2022-03-10T03.22.39Z
[2022/03/10 03:22:39.860 +00:00] [INFO] [collector.go:67] ["Database restore failed summary"] [total-ranges=0] [ranges-succeed=0] [ranges-failed=0]
Error: running BR in incompatible version of cluster, if you believe it's OK, use --check-requirements=false to skip.: TiKV node dst-tidb-tikv-0.dst-tidb-tikv-peer.fb-testbed-comp-rlj79.svc:20160 version 5.4.0 and BR v6.0.0-nightly major version mismatch, please use the same version of BR: [BR:Common:ErrVersionMismatch]version mismatch

4. What is your TiDB version? (Required)

/ # /br -V
Release Version: v6.0.0-nightly
Git Commit Hash: 77730b6
Git Branch: heads/refs/tags/v6.0.0-nightly
Go Version: go1.16.4
UTC Build Time: 2022-03-09 18:08:00
Race Enabled: false

/ # /tikv-server -V
TiKV
Release Version: 5.4.0
Edition: Community
Git Commit Hash: b5262299604df88711d9ed4b84d43e9c507749a2
Git Commit Branch: heads/refs/tags/v5.4.0
UTC Build Time: 2022-01-25 07:14:08
Rust Version: rustc 1.56.0-nightly (2faabf579 2021-07-27)
Enable Features: jemalloc mem-profiling portable sse test-engines-rocksdb cloud-aws cloud-gcp cloud-azure
Profile: dist_release

[fubinzh]

I noticed we have below description in https://docs.pingcap.com/tidb/stable/backup-and-restore-tool#version-check:

====
Before performing backup and restore, BR compares and checks the TiDB cluster version and the BR version. If there is a major-version mismatch (for example, BR v4.x and TiDB v5.x), BR prompts a reminder to exit. To forcibly skip the version check, you can set --check-requirements=false.