tests CHANGE rename config.h to tests_config.h

Make the tests' config header name clearly connected with tests. The
config.h is supposed to be connected with sources.
diff --git a/tests/utests/data/test_validation.c b/tests/utests/data/test_validation.c
index b1dc2f4..2045a3a 100644
--- a/tests/utests/data/test_validation.c
+++ b/tests/utests/data/test_validation.c
@@ -22,7 +22,7 @@
 #include "out.h"
 #include "parser_data.h"
 #include "printer_data.h"
-#include "tests/config.h"
+#include "tests_config.h"
 #include "tree_data_internal.h"
 #include "tree_schema.h"