sweet/harnesses: make git less chatty more

In CL 600060, I made most calls to git less chatty, but missed one.

Change-Id: Ieec2b7216467c5d5f40a25c20506eca945fa6ada
Reviewed-on: https://go-review.googlesource.com/c/benchmarks/+/600115
Auto-Submit: Austin Clements <austin@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
1 file changed