internal/trace: increment sync counter before final Sync on error
CL 648195 was supposed to have fixed #71615, but it didn't include an
update to r.syncs. I can confirm this CL fixes the issue even when
running the test many times in a row.
Fixes #71615.
Change-Id: I97db3d639dc5bc8648a191696f90b0e5087307c8
Reviewed-on: https://go-review.googlesource.com/c/go/+/648315
Auto-Submit: Michael Knyszek <mknyszek@google.com> Reviewed-by: Cherry Mui <cherryyz@google.com>
TryBot-Bypass: Michael Knyszek <mknyszek@google.com>