[FLINK-38830][runtime] Handle duplicate AddColumnEvent gracefully to prevent pipeline crashes #2010

Job	Run time
License Check	4m 28s
Common Unit Tests / test (11, generic, core)	13m 8s
Pipeline Unit Tests / test (11, generic, doris, elasticsearch, fluss, hudi, iceberg, kafka, maxcompute, mysql-pipeline,...	22m 17s
Source E2E Tests / test (11, 1.19.3, source_e2e)	22m 41s
Source Unit Tests / test (11, generic, oracle, sqlserver)	47m 31s
Source Unit Tests / test (11, generic, postgres-source, oceanbase-source, tidb, vitess)	36m 51s
Source Unit Tests / test (11, generic, db2, mongodb)	43m 43s
Source Unit Tests / test (11, generic, mysql-source)	46m 35s
Source E2E Tests / test (11, 1.20.3, source_e2e)	22m 45s
Pipeline E2E Tests (4-Parallelism) / test (11, 1.19.3, pipeline_e2e)	1h 16m 12s
Pipeline E2E Tests (1-Parallelism) / test (11, 1.19.3, pipeline_e2e)	1h 20m 43s
Pipeline E2E Tests (1-Parallelism) / test (11, 1.20.3, pipeline_e2e)	1h 18m 44s
Pipeline E2E Tests (4-Parallelism) / test (11, 1.20.3, pipeline_e2e)	1h 13m 18s
	9h 28m 56s

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