op-exporter: don't use the deprecated function `ioutil.ReadFile` (#8753)

op-exporter/main.go

@@ -3,7 +3,6 @@ package main
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
 	"net/http"
 	"os"
 	"strings"
@@ -143,7 +142,7 @@ func main() {
 }
 
 func getSequencerVersion(health *healthCheck, client *kubernetes.Clientset) {
-	ns, err := ioutil.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/namespace")
+	ns, err := os.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/namespace")
 	if err != nil {
 		log.Fatalf("Unable to read namespace file: %s", err)
 	}