When sub_process encounters a row skip, it should skip its internal row, and not bubble up to the outer row

Problem/Motivation

If a process executed inside of a sub process process plugin throws a MigrateSkipRowException, the expected behavior is to catch that exception in sub_process and skip the current row that sub_process is processing. Currently the exception is not caught, and is bubbled all the way up to the main executable and skips the entire outer row. This is buggy behavior and should be fixed.

Steps to reproduce

Proposed resolution

We are looking at changing the row skip mechanism in #3247718: Allow process plugins to flag a row to be skipped, but fixing this bug is out of scope for that issue. We can fix the bug now, or afterwards depending on which issue gets committed first.

Remaining tasks

User interface changes

API changes

Data model changes

Release notes snippet