internal/gitfs: close response body in Repo.handshake

This was missed in CL 328213.

Change-Id: If62b9ee842b4b89725915ae74f755e66073264bd
Reviewed-on: https://go-review.googlesource.com/c/website/+/352329
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Rhys Hiltner <rhys.hiltner@gmail.com>

internal/gitfs/git.go

@@ -41,6 +41,7 @@ func (r *Repo) handshake() error {
 	if err != nil {
 		return fmt.Errorf("handshake: %v", err)
 	}
+	defer resp.Body.Close()
 	data, err := io.ReadAll(resp.Body)
 	if resp.StatusCode != 200 {
 		return fmt.Errorf("handshake: %v\n%s", resp.Status, data)