test: unflake TestWebSocket.shouldEmitError (#976)

Author: yury-s

playwright/src/test/java/com/microsoft/playwright/TestWebSocket.java

@@ -25,6 +25,7 @@
 import java.time.Instant;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Consumer;
 
 import static java.util.Arrays.asList;
 import static org.junit.jupiter.api.Assertions.*;
@@ -139,9 +140,13 @@ void shouldEmitError() {
     boolean[] socketError = {false};
     String[] error = {null};
     page.onWebSocket(ws -> {
-      ws.onSocketError(e -> {
-        error[0] = e;
-        socketError[0] = true;
+      ws.onSocketError(new Consumer<String>() {
+        @Override
+        public void accept(String e) {
+          ws.offSocketError(this);
+          error[0] = e;
+          socketError[0] = true;
+        }
       });
     });
     page.evaluate("port => {\n" +