The 'version' value was not being refreshed in various MySQL dashboards.

STR:

• Install PMM2 server dev-latest with added Percona Server
• Open MySQL Instance Summary dashboard
• Upgrade MySQL Server (e.g. 8.0.18-9 -> 8.0.19)
• Take a look at opened MySQL Instance Summary dashboard

Given result:
Singlestat still shown the previous MySQL version.

Expected result:
Correct version is shown if time range is changed.

Solution:
The mentioned singlestat is formed by the variable $version.
It's used function label_values in formula. This function returns a list of label names for selected time range.
So we got all mysql versions that were detected for this service during a selected time range.

We can try to replace function label_values by another function query_result(query).
It returns a list of Prometheus query result for the query. So we would get the last value only.