Google BigQuery Data Source: Variable doesn't get values

When I make a simple table panel with BigQuery - I get results.
When I run the exact same query in variable - the variable is empty.
Although Grafana says: "This query will process X B when run.", still the variable doesn't get values.

I tried to look inside "Network" pane from Dev Tools when I trigger the variable query - and I can see the results. But nothing is presented within the variable.

Worth noting, when I run this query for example:
`SELECT table_name
FROM .INFORMATION_SCHEMA.TABLES`
The variable gets values. Just with my query - doesn't.

I see [that](https://community.grafana.com/t/bigquery-data-source-migration-panel-data-works-template-variables-empty-after-doitintl-official-plugin/154811), but there is no any answer that works.

I use v3.1.5 of the plugin, with Grafna OSS v12.3.1

Reproduce the issue with Grafana OSS 12.3.1 and the BigQuery plugin 3.1.5, comparing the same query in a table panel and a template variable. Inspect the variable request and returned data in the browser Network pane, then trace how that response is consumed; done means the variable displays values for the reported query as well as INFORMATION_SCHEMA.TABLES queries.

Written by the indexing model from the issue text.