integration/c8d: Skip TestBuildSquashParent

`docker build --squash` is an experimental feature which is not
implemented for containerd image store.

Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>

integration/build/build_squash_test.go

@@ -20,6 +20,7 @@ import (
 
 func TestBuildSquashParent(t *testing.T) {
 	skip.If(t, testEnv.DaemonInfo.OSType == "windows")
+	skip.If(t, testEnv.UsingSnapshotter(), "squash is not implemented for containerd image store")
 
 	ctx := testutil.StartSpan(baseContext, t)