Updated the use of atomic.Uint32 to atomic.Bool for sync package.

Change-Id: Ib8da66fea86ef06e1427ac5118016b96fbcda6b1
GitHub-Last-Rev: d36e0f431fcde988f90badf86bbf04a18a411947
GitHub-Pull-Request: golang/go#73447
Reviewed-on: https://go-review.googlesource.com/c/go/+/666895


Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Jorropo <jorropo.pgm@gmail.com>