[FLINK-38267][checkpoint] Fix the test timeout for UnalignedCheckpointRescaleWithMixedExchangesITCase.testRescaleFromUnalignedCheckpoint

When one task has multiple inputs, and the unaligned checkpoint will be disabled for all inputs once one input exchange does not support unaligned checkpoint. It caused no inflight buffers, but UnalignedCheckpointRescaleWithMixedExchangesITCase.testRescaleFromUnalignedCheckpoint always wait for checkpoint with inflight buffers.

Explicitly specifying rebalance can avoid the forward exchange.

Author: 1996fanrui

flink-tests/src/test/java/org/apache/flink/test/checkpointing/UnalignedCheckpointRescaleWithMixedExchangesITCase.java

@@ -231,7 +231,7 @@ private static JobClient createMultiInputDAG(StreamExecutionEnvironment env) thr
 
         sourceStream1
                 .rebalance()
-                .connect(forwardedStream)
+                .connect(forwardedStream.rebalance())
                 .map(new SleepingCoMap())
                 .name("Co-Map")
                 .setParallelism(getRandomParallelism());
@@ -308,7 +308,7 @@ private static JobClient createMixedComplexityDAG(StreamExecutionEnvironment env
         DataStream<Long> multiInputMap =
                 sourceStream1
                         .rebalance()
-                        .connect(forwardedStream)
+                        .connect(forwardedStream.rebalance())
                         .map(new SleepingCoMap())
                         .name("Co-Map")
                         .setParallelism(getRandomParallelism());