Update gomod and vendor

vendor/github.com/moby/buildkit/executor/oci/spec.go

@@ -0,0 +1,13 @@
+package oci
+
+// ProcMode configures PID namespaces
+type ProcessMode int
+
+const (
+	// ProcessSandbox unshares pidns and mount procfs.
+	ProcessSandbox ProcessMode = iota
+	// NoProcessSandbox uses host pidns and bind-mount procfs.
+	// Note that NoProcessSandbox allows build containers to kill (and potentially ptrace) an arbitrary process in the BuildKit host namespace.
+	// NoProcessSandbox should be enabled only when the BuildKit is running in a container as an unprivileged user.
+	NoProcessSandbox
+)