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/archiver/testing.go

@@ -2,7 +2,6 @@ package archiver
 
 import (
 	"context"
-	"io/ioutil"
 	"os"
 	"path"
 	"path/filepath"
@@ -73,7 +72,7 @@ func TestCreateFiles(t testing.TB, target string, dir TestDir) {
 
 		switch it := item.(type) {
 		case TestFile:
-			err := ioutil.WriteFile(targetPath, []byte(it.Content), 0644)
+			err := os.WriteFile(targetPath, []byte(it.Content), 0644)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -152,7 +151,7 @@ func TestEnsureFiles(t testing.TB, target string, dir TestDir) {
 				return nil
 			}
 
-			content, err := ioutil.ReadFile(path)
+			content, err := os.ReadFile(path)
 			if err != nil {
 				return err
 			}