Fix missing #include.

--- graphite2-1.3.14/tests/featuremap/featuremaptest.cpp	2020-04-01 03:53:13.000000000 +0100
+++ graphite2-1.3.14/tests/featuremap/featuremaptest.cpp	2025-07-04 02:29:27.101884084 +0100
@@ -21,6 +21,7 @@
 */
 #include <cassert>
 #include <cstdlib>
+#include <cstdint>
 #include <fstream>
 #include <iostream>
 #include <map>