Attn: Added needed cstdint include

Moving to gcc13 requires explicitly including some
previously indirectly resolved includes. In this
case cstdint was needed to resolve uint32_t type.

Change-Id: I0d2a20a4ccb2aaef6564f197be15bc2e26641976
Signed-off-by: Ben Tyner <ben.tyner@ibm.com>
diff --git a/attn/attn_handler.hpp b/attn/attn_handler.hpp
index af6ebc6..f7ac3e8 100644
--- a/attn/attn_handler.hpp
+++ b/attn/attn_handler.hpp
@@ -2,6 +2,8 @@
 
 #include <attn/attn_config.hpp>
 
+#include <cstdint>
+
 namespace attn
 {
 /** @brief Attention global status bits */