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

diff --git a/tests/utests/data/test_validation.c b/tests/utests/data/test_validation.c
index fde40de..8934de2 100644
--- a/tests/utests/data/test_validation.c
+++ b/tests/utests/data/test_validation.c
@@ -24,6 +24,7 @@
 
 #include "../../src/context.h"
 #include "../../src/tree_data_internal.h"
+#include "../../src/printer.h"
 #include "../../src/printer_data.h"
 
 #define BUFSIZE 1024