[flink] Work around Flink 2.3 ON CONFLICT validation in Delta Join ITCase

Flink 2.3 introduces ExecutionConfigOptions.TABLE_EXEC_SINK_REQUIRE_ON_CONFLICT
(table.exec.sink.require-on-conflict), defaulting to true. In
FlinkChangelogModeInferenceProgram, this triggers a ValidationException
("upsert key differs from primary key") before the
StreamPhysicalDeltaJoinForceValidator runs, so the Delta Join ITCases can no
longer reach the original "doesn't support to do delta join optimization"
error path.

Disable the option in Flink23DeltaJoinITCase#beforeEach so the existing
assertions remain valid. Production-side impact (real Fluss users hitting
this on multi-table joins / group-by + insert) is left to community
discussion.

Signed-off-by: Pei Yu <125331682@qq.com>

Author: sd4324530

fluss-flink/fluss-flink-2.3/src/test/java/org/apache/fluss/flink/source/Flink23DeltaJoinITCase.java

@@ -82,6 +82,13 @@ public void beforeEach() {
                 .set(
                         OptimizerConfigOptions.TABLE_OPTIMIZER_DELTA_JOIN_STRATEGY,
                         OptimizerConfigOptions.DeltaJoinStrategy.FORCE);
+        // Flink 2.3 introduces ExecutionConfigOptions.TABLE_EXEC_SINK_REQUIRE_ON_CONFLICT
+        // (default true), which makes FlinkChangelogModeInferenceProgram throw a
+        // "upsert key differs from primary key" ValidationException before the
+        // StreamPhysicalDeltaJoinForceValidator runs. Disable it here so the existing
+        // delta-join "doesn't support to do delta join optimization" error remains
+        // reachable from these tests.
+        tEnv.getConfig().set(ExecutionConfigOptions.TABLE_EXEC_SINK_REQUIRE_ON_CONFLICT, false);
     }
 
     @AfterEach