tso client: Do not fallback to group 0 if no tso service is available #9883
Description
Bug Report
What did you do?
In the prod env, the TSO group's primary lease expired and a re-election was triggered due to pressure issues.
What did you expect to see?
After a new TSO group primary is normally elected, TSO requests return to normal.
What did you see instead?
TiDB reported an error indicating a fallback to group 0.
What version of PD are you using (pd-server -V)?
pd-cse 8.5