System.currentTimeMillis() should not be used for time comparisons in SeekableStreamIndexTaskRunner

https://github.com/apache/incubator-druid/blob/fba92ae469b512cca6cdf86ffc1c1a2090808453/indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/SeekableStreamIndexTaskRunner.java#L709

See https://github.com/code-review-checklists/java-concurrency#time-going-backward

/cc @jihoonson

Thanks to @richardstartin for pointing this out.

Open indexing-service/src/main/java/org/apache/druid/indexing/seekablestream/SeekableStreamIndexTaskRunner.java at line 709 and read the linked Java concurrency guidance on time going backward. Identify the time comparison using System.currentTimeMillis(); done when that comparison no longer depends on wall-clock time and the runner's behavior remains correct.

Written by the indexing model from the issue text.