Replace deprecated ioutil with io and os

https://pkg.go.dev/io/ioutil is deprecated since Go 1.16.

hugolib/resource_chain_test.go

@@ -16,7 +16,6 @@ package hugolib
 import (
 	"fmt"
 	"io"
-	"io/ioutil"
 	"math/rand"
 	"net/http"
 	"net/http/httptest"
@@ -305,7 +304,7 @@ func TestResourceChains(t *testing.T) {
 		case "/post":
 			w.Header().Set("Content-Type", "text/plain")
 			if r.Method == http.MethodPost {
-				body, err := ioutil.ReadAll(r.Body)
+				body, err := io.ReadAll(r.Body)
 				if err != nil {
 					http.Error(w, "Internal server error", http.StatusInternalServerError)
 					return

hugolib/site_stats_test.go

@@ -16,7 +16,7 @@ package hugolib
 import (
 	"bytes"
 	"fmt"
-	"io/ioutil"
+	"io"
 	"testing"
 
 	"github.com/gohugoio/hugo/helpers"
@@ -87,8 +87,8 @@ aliases: [/Ali%d]
 		h.Sites[1].PathSpec.ProcessingStats,
 	}
 
-	stats[0].Table(ioutil.Discard)
-	stats[1].Table(ioutil.Discard)
+	stats[0].Table(io.Discard)
+	stats[1].Table(io.Discard)
 
 	var buff bytes.Buffer
 

hugolib/site_test.go

@@ -17,7 +17,6 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -1094,7 +1093,7 @@ ABC.
 	b.Build(BuildCfg{})
 
 	contentMem := b.FileContent(statsFilename)
-	cb, err := ioutil.ReadFile(statsFilename)
+	cb, err := os.ReadFile(statsFilename)
 	b.Assert(err, qt.IsNil)
 	contentFile := string(cb)