libyang CHANGE headers includes cleanup using include-what-you-use tool (#1098)

diff --git a/tests/utests/test_xpath.c b/tests/utests/test_xpath.c
index 8f1b533..1552512 100644
--- a/tests/utests/test_xpath.c
+++ b/tests/utests/test_xpath.c
@@ -23,6 +23,7 @@
 #include <string.h>
 
 #include "../../src/context.h"
+#include "../../src/set.h"
 #include "../../src/tree_data.h"
 #include "../../src/tree_schema.h"