refactor: use slices package for sort (#10132)

The sort package is still used in places that were not trivial to
change. Since Go 1.21 slices package can be uswed for sort. See
https://go.dev/doc/go1.21#slices

### Purpose

Make some progress with the migration to a more up-to-date syntax.

lib/config/config_test.go

@@ -17,7 +17,7 @@ import (
 	"path/filepath"
 	"reflect"
 	"runtime"
-	"sort"
+	"slices"
 	"strings"
 	"testing"
 
@@ -911,7 +911,7 @@ func TestV14ListenAddressesMigration(t *testing.T) {
 			t.Error("Configuration was not converted")
 		}
 
-		sort.Strings(tc[2])
+		slices.Sort(tc[2])
 		if !reflect.DeepEqual(cfg.Options.RawListenAddresses, tc[2]) {
 			t.Errorf("Migration error; actual %#v != expected %#v", cfg.Options.RawListenAddresses, tc[2])
 		}