tdb2: fix compile of test/run-check-callback.c

ccan/tdb2/test/run-check-callback.c

@@ -6,6 +6,7 @@
 #include <ccan/tdb2/check.c>
 #include <ccan/tdb2/traverse.c>
 #include <ccan/tdb2/transaction.c>
+#include <ccan/tdb2/open.c>
 #include <ccan/tap/tap.h>
 #include "logging.h"