Datasource: Stackdriver - Unable to get labels value from "metadata.system_labels.*" labels in dashboard variable query

### What happened? Previously, in version 11.4.4, I was able to configure dashboard variables with a Stackdriver label value. But since I bumped grafana to version 12.1.0 it is no longer working. All other labels that does not start with `metadata.system_labels.*` are working properly, but when it starts with `metadata.system_labels.*` I can't get any values. Note: I am able to get the label value using the explore page and the following query : ``` sum by (metadata_system_name, project_id)({"__name__"="agent.googleapis.com/disk/percent_used","monitored_resource"="gce_instance","state"!="free"}) ``` My configuration is the following : ``` --- my-variable Variable type: Query --- Query options Data source: Stackdriver Query type: Label Values Project: xxx Service: agent Metric Type: Disk utilization Label Key: metadata.system_labels.name ``` ### What did you expect to happen? The variable query to return the content of the label. ### Did this work before? Yes, in version 11.4.4 . ### How do we reproduce it? 1. Add a stackdriver datasource to your grafana instance. 2. Deploy an VM instance in gcp. 3. Make sure grafana can access the VM instance metrics trough the Stackdriver datasource. Ex. by using this query in the "Explore" page : `sum by (metadata_system_name, project_id)({"__name__"="agent.googleapis.com/disk/percent_used","monitored_resource"="gce_instance","state"!="free"})` 4. Create a dashboard and add a new `Query` variable and setup it like this: ``` Variable type: Query --- Query options Data source: Stackdriver Query type: Label Values Project: xxx Service: agent Metric Type: Disk utilization Label Key: **metadata.system_labels.name** ``` 5. Click `Run query` 6. Expect to see you instance name. ### Is the bug inside a dashboard panel? No. ### Environment (with versions)? Grafana: 12.1.0 OS: Docker container from docker hub. Browser: Firefox 141.0 (64-bit) on Windows 10 ### Grafana platform? Docker ### Datasource(s)? Stackdriver