memfs: Fix test which may error due to Windows timer resolution

More information can be found on upstream documentation:
https://github.com/golang/go/blob/7255b949202bb752b6525aa24cb636ceaf24e4d1/src/time/time.go#L85-L90

Signed-off-by: Paulo Gomes <[email protected]>

Author: pjbgf

memfs/memory_test.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"runtime"
 	"testing"
+	"time"
 
 	"github.com/go-git/go-billy/v5"
 	"github.com/go-git/go-billy/v5/util"
@@ -34,6 +35,10 @@ func TestModTime(t *testing.T) {
 	_, err := fs.Create("/file1")
 	require.NoError(t, err)
 
+	if runtime.GOOS == "windows" {
+		time.Sleep(20 * time.Millisecond)
+	}
+
 	_, err = fs.Create("/file2")
 	require.NoError(t, err)