[FLINK-30960] Fix a corner case oom error

[bs352]

I fixed a corner case out-of-memory error when we use a timed flushing interval, where the scheduler thread could repeatly throw a new RuntimeException wrapping the previous one as cause. This could lead to an infinite object reference chain.

[boring-cyborg[bot]]

Thanks for opening this pull request! Please check out our contributing guidelines. (https://flink.apache.org/contributing/how-to-contribute.html)

[davidradl]

is this the same as https://github.com/apache/flink-connector-jdbc/pull/5