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>
diff --git a/sweet/harnesses/common.go b/sweet/harnesses/common.go
index 84c739d..ac9f832 100644
--- a/sweet/harnesses/common.go
+++ b/sweet/harnesses/common.go
@@ -14,7 +14,8 @@
 )
 
 func gitShallowClone(dir, url, ref string) error {
-	cmd := exec.Command("git", "clone", "--depth", "1", "-b", ref, url, dir)
+	// Git 2.46+ has a global --no-advice flag, but that's extremely recent as of this writing.
+	cmd := exec.Command("git", "-c", "advice.detachedHead=false", "clone", "--depth", "1", "-b", ref, url, dir)
 	log.TraceCommand(cmd, false)
 	cmd.Stderr = os.Stderr
 	_, err := cmd.Output()
@@ -28,7 +29,6 @@
 	if _, err := cloneCmd.Output(); err != nil {
 		return err
 	}
-	// Git 2.46+ has a global --no-advice flag, but that's extremely recent as of this writing.
 	checkoutCmd := exec.Command("git", "-C", dir, "-c", "advice.detachedHead=false", "checkout", hash)
 	log.TraceCommand(checkoutCmd, false)
 	checkoutCmd.Stderr = os.Stderr