Temporarily disable TestCheckpoint

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

integration/container/checkpoint_test.go

@@ -30,6 +30,7 @@ func containerExec(t *testing.T, client client.APIClient, cID string, cmd []stri
 }
 
 func TestCheckpoint(t *testing.T) {
+	t.Skip("TestCheckpoint is broken; see https://github.com/moby/moby/issues/38963")
 	skip.If(t, testEnv.DaemonInfo.OSType == "windows")
 	skip.If(t, !testEnv.DaemonInfo.ExperimentalBuild)