Check GPUAdapterInfo.isFallbackAdapter on explicit fallback request (#4483)

According to specification a fallback adapter may still be returned
if forceFallbackAdapter is set to false and either no other appropriate
adapter is available or the user agent chooses to return a fallback adapter.
https://gpuweb.github.io/gpuweb/#dom-gpurequestadapteroptions-forcefallbackadapter

Therefore, checking whether an adapter is a fallback adapter should only
be performed if forceFallbackAdapter is true.

Issue: #4480

Signed-off-by: Andrei Volykhin <[email protected]>

Author: tharkum

src/webgpu/api/operation/adapter/requestAdapter.spec.ts

@@ -124,7 +124,10 @@ g.test('requestAdapter')
       return;
     }
 
-    t.expect(adapter.info.isFallbackAdapter === Boolean(forceFallbackAdapter));
+    // Only a fallback adapter may be returned when forceFallbackAdapter is true.
+    if (forceFallbackAdapter === true) {
+      t.expect(adapter.info.isFallbackAdapter === true);
+    }
     await testAdapter(t, adapter);
   });