During the rolling upgrade from 2.5 to 2.6, the 2.5 coordinator detects
newly started 2.6 proxies. However, 2.6 proxies do not sync timetick,
which leads to timetick delay. This PR ignores 2.6 proxies to prevent
ttDelay during the upgrade process.
issue: https://github.com/milvus-io/milvus/issues/43518
Signed-off-by: bigsheeper <yihao.dai@zilliz.com>