Fix test to match actual exception propagation behavior

Co-authored-by: mykaul <4655593+mykaul@users.noreply.github.com>

Author: Copilot

core/src/test/java/com/datastax/oss/driver/internal/core/util/concurrent/CompletableFuturesTest.java

@@ -71,7 +71,6 @@ public void should_propagate_exception_with_timeout() {
     RuntimeException error = new RuntimeException("test error");
     future.completeExceptionally(error);
     assertThatThrownBy(() -> CompletableFutures.getUninterruptibly(future, Duration.ofSeconds(1)))
-        .isInstanceOf(DriverExecutionException.class)
-        .hasCause(error);
+        .isEqualTo(error);
   }
 }