When calling Git.execute, including indirectly through the dynamic methods of a Git object, passing a non-None value of output_stream suppresses the effect of kill_after_timeout. The threading.Timer object is created with the local kill_process function as its callback, but start is never called on it.

This situation appears not entirely intentional, because:

• The "watchdog" Timer is created, even though it is never used.
• The docstring, even as it documents that as_process suppresses kill_after_timeout (and that as_process suppresses output_stream), does not mention any effect of output_stream on kill_after_timeout.

So either kill_after_timeout should be honored even when output_stream is used, or the docstring should be updated to mention that it does not (and the code possibly modified to not create the Timer object in the case that it is unused).

I am not sure which change should be made, so I'm opening this rather than a PR to propose one of them.

This is effectively separate from #1756. (One quality this shares with #1756 is that it is relevant only to the behavior of Git.execute and functions that use it. Functions that use handle_process_output are unaffected; its kill_after_timeout is implemented differently with nonequivalent behavior and separate code. handle_process_output also does not take an output_stream argument.)