qe: fix a compiler warning when driver adapters are disabled (#4727)

Fixes the following warning when compiling the tests:

```
warning: unused variable: `adapter`
  --> query-engine/request-handlers/src/load_executor.rs:28:29
   |
28 |         ConnectorKind::Js { adapter, _phantom } => {
   |                             ^^^^^^^ help: try ignoring the field: `adapter: _`
   |
   = note: `#[warn(unused_variables)]` on by default
```

query-engine/request-handlers/src/load_executor.rs

@@ -25,14 +25,14 @@ pub async fn load(
     features: PreviewFeatures,
 ) -> query_core::Result<Box<dyn QueryExecutor + Send + Sync + 'static>> {
     match connector_kind {
-        ConnectorKind::Js { adapter, _phantom } => {
-            #[cfg(not(feature = "driver-adapters"))]
+        #[cfg(not(feature = "driver-adapters"))]
+        ConnectorKind::Js { .. } => {
             panic!("Driver adapters are not enabled, but connector mode is set to JS");
-
-            #[cfg(feature = "driver-adapters")]
-            driver_adapter(adapter, features).await
         }
 
+        #[cfg(feature = "driver-adapters")]
+        ConnectorKind::Js { adapter, _phantom } => driver_adapter(adapter, features).await,
+
         #[cfg(feature = "native")]
         ConnectorKind::Rust { url, datasource } => {
             if let Ok(value) = env::var("PRISMA_DISABLE_QUAINT_EXECUTORS") {