vendor: update buildkit to master@9624ab4

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

vendor/github.com/moby/buildkit/util/system/atime_unix.go

@@ -0,0 +1,21 @@
+//go:build !windows
+// +build !windows
+
+package system
+
+import (
+	iofs "io/fs"
+	"syscall"
+	"time"
+
+	"github.com/containerd/continuity/fs"
+	"github.com/pkg/errors"
+)
+
+func Atime(st iofs.FileInfo) (time.Time, error) {
+	stSys, ok := st.Sys().(*syscall.Stat_t)
+	if !ok {
+		return time.Time{}, errors.Errorf("expected st.Sys() to be *syscall.Stat_t, got %T", st.Sys())
+	}
+	return fs.StatATimeAsTime(stSys), nil
+}