[v9.3.x] @grafana/runtime: Avoid calling applyTemplateVariables for the wrong datasource (#59029)

@grafana/runtime: Avoid calling applyTemplateVariables for the wrong datasource (#57921)

(cherry picked from commit 448358ac66)

Co-authored-by: Andres Martinez Gotor <andres.martinez@grafana.com>

packages/grafana-runtime/src/utils/DataSourceWithBackend.ts

@@ -133,6 +133,7 @@ class DataSourceWithBackend<
     const queries = targets.map((q) => {
       let datasource = this.getRef();
       let datasourceId = this.id;
+      let shouldApplyTemplateVariables = true;
 
       if (isExpressionReference(q.datasource)) {
         hasExpr = true;
@@ -149,8 +150,15 @@ class DataSourceWithBackend<
           throw new Error(`Unknown Datasource: ${JSON.stringify(q.datasource)}`);
         }
 
-        datasource = ds.rawRef ?? getDataSourceRef(ds);
-        datasourceId = ds.id;
+        const dsRef = ds.rawRef ?? getDataSourceRef(ds);
+        const dsId = ds.id;
+        if (dsRef.uid !== datasource.uid || datasourceId !== dsId) {
+          datasource = dsRef;
+          datasourceId = dsId;
+          // If the query is using a different datasource, we would need to retrieve the datasource
+          // instance (async) and apply the template variables but it seems it's not necessary for now.
+          shouldApplyTemplateVariables = false;
+        }
       }
       if (datasource.type?.length) {
         pluginIDs.add(datasource.type);
@@ -159,7 +167,7 @@ class DataSourceWithBackend<
         dsUIDs.add(datasource.uid);
       }
       return {
-        ...this.applyTemplateVariables(q, request.scopedVars),
+        ...(shouldApplyTemplateVariables ? this.applyTemplateVariables(q, request.scopedVars) : q),
         datasource,
         datasourceId, // deprecated!
         intervalMs,