Workaround:
Create new “structure” measurement with records with tags (timestamp of the records is not important):
value,text
----------
Partner,Production
Sandbox,Sandbox
unknown,unknown
Create 1st dashboard variable text from text tag values (SHOW TAG VALUES WITH KEY = "text").
Create 2nd hidden dashboard variable value with query SHOW TAG VALUES WITH KEY = "value" WHERE "text"=$text.
=> Grafana will select in the background correct value for your InfluxDB querier - you have to use $value variable in your queries.