GH-34367: [Java] Fix build error from sequential merges (#34368)

### Rationale for this change

I broke main by merging two PRs in quick succession that unfortunately didn't work together.

### What changes are included in this PR?

Fix the build error.

### Are these changes tested?

N/A

### Are there any user-facing changes?

No, test code only
* Closes: #34367

Authored-by: David Li <li.davidm96@gmail.com>
Signed-off-by: David Li <li.davidm96@gmail.com>

java/flight/flight-core/src/test/java/org/apache/arrow/flight/client/CustomHeaderTest.java

@@ -35,6 +35,7 @@
 import org.apache.arrow.flight.FlightStream;
 import org.apache.arrow.flight.FlightTestUtil;
 import org.apache.arrow.flight.HeaderCallOption;
+import org.apache.arrow.flight.Location;
 import org.apache.arrow.flight.NoOpFlightProducer;
 import org.apache.arrow.flight.RequestContext;
 import org.apache.arrow.flight.SyncPutListener;
@@ -74,10 +75,12 @@ public void setUp() throws Exception {
       callHeaders.insert(entry.getKey(), entry.getValue());
     }
     headers = new HeaderCallOption(callHeaders);
-    server = FlightTestUtil.getStartedServer(location ->
-            FlightServer.builder(allocator, location, new NoOpFlightProducer())
-                    .middleware(FlightServerMiddleware.Key.of("customHeader"), headersMiddleware)
-                    .build());
+    server = FlightServer.builder(allocator,
+            Location.forGrpcInsecure(FlightTestUtil.LOCALHOST, /*port*/ 0),
+            new NoOpFlightProducer())
+        .middleware(FlightServerMiddleware.Key.of("customHeader"), headersMiddleware)
+        .build();
+    server.start();
     client = FlightClient.builder(allocator, server.getLocation()).build();
   }