ccanlint: fix --test-dep-graph

Broken by 758ab1f4 "ccanlint: drop -d, interpret any arguments as
directories, and allow multiple."

tools/ccanlint/ccanlint.c

@@ -403,6 +403,7 @@ static void test_dgraph_edges(struct list_head *tests)
 
 static char *test_dependency_graph(void *arg)
 {
+	init_tests();
 	puts("digraph G {");
 
 	test_dgraph_vertices(&compulsory_tests, ", style=filled, fillcolor=yellow");