sync: fix connection error on macOS

With a large number of sync workers, the sync process may fail on
macOS due to connection errors. The root cause is that multiple
workers may attempt to connect to the multiprocessing manager server
at the same time when handling the first job. This can lead to
connection failures if there are too many pending connections, exceeding
the socket listening backlog.

Bug: 377538810
Change-Id: I1924d318d076ca3be61d75daa37bfa8d7dc23ed7
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/441541


Tested-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>