Add SarahFrench to on vacation list (GoogleCloudPlatform#10189)

.ci/magician/github/membership.go

@@ -46,7 +46,9 @@ var (
 	trustedContributors = []string{}
 
 	// This is for reviewers who are "on vacation": will not receive new review assignments but will still receive re-requests for assigned PRs.
-	onVacationReviewers = []string{}
+	onVacationReviewers = []string{
+		"SarahFrench",
+	}
 )
 
 type UserType int64