Replace most usages of ioutil with the underlying function

The ioutil functions are deprecated since Go 1.17 and only wrap another
library function. Thus directly call the underlying function.

This commit only mechanically replaces the function calls.

internal/backend/sftp/sftp_test.go

@@ -3,7 +3,6 @@ package sftp_test
 import (
 	"context"
 	"fmt"
-	"io/ioutil"
 	"os"
 	"path/filepath"
 	"strings"
@@ -34,7 +33,7 @@ func newTestSuite(t testing.TB) *test.Suite {
 	return &test.Suite{
 		// NewConfig returns a config for a new temporary backend that will be used in tests.
 		NewConfig: func() (interface{}, error) {
-			dir, err := ioutil.TempDir(rtest.TestTempDir, "restic-test-sftp-")
+			dir, err := os.MkdirTemp(rtest.TestTempDir, "restic-test-sftp-")
 			if err != nil {
 				t.Fatal(err)
 			}