testsuite: include stdio.h

It's used in the log macros so include it.
diff --git a/testsuite/testsuite.h b/testsuite/testsuite.h
index 3bd74f3..bb0eb50 100644
--- a/testsuite/testsuite.h
+++ b/testsuite/testsuite.h
@@ -19,6 +19,7 @@
 
 #include <stdbool.h>
 #include <stdarg.h>
+#include <stdio.h>
 
 #include <shared/macro.h>