use correct timer for last health check

redis.go

@@ -1366,11 +1366,13 @@ func (c *baseClient) processPushNotifications(ctx context.Context, cn *pool.Conn
 	// If the connection was health-checked within the last 5 seconds, we can skip the
 	// expensive syscall since the health check already verified no unexpected data.
 	// This is safe because:
+	// 0. lastHealthCheckNs is set in pool/conn.go:putConn() after a successful health check
 	// 1. Health check (connCheck) uses the same syscall (Recvfrom with MSG_PEEK)
 	// 2. If push notifications arrived, they would have been detected by health check
 	// 3. 5 seconds is short enough that connection state is still fresh
 	// 4. Push notifications will be processed by the next WithReader call
-	lastHealthCheckNs := cn.UsedAtNs()
+	// used it is set on getConn, so we should use another timer (lastPutAt?)
+	lastHealthCheckNs := cn.LastPutAtNs()
 	if lastHealthCheckNs > 0 {
 		// Use pool's cached time to avoid expensive time.Now() syscall
 		nowNs := pool.GetCachedTimeNs()