Fix building with GCC 13.

Fixes the following issue:
base64.hpp:23:49: error: 'uint8_t' was not declared in this scope

and:
deprecation.hpp:20:22: error: found ':' in nested-name-specifier, expected '::'

src/deprecation.hpp

@@ -14,6 +14,7 @@
 
 #pragma once
 
+#include <cstdint>
 #include <string>
 
 /** See https://wiki.wesnoth.org/CompatibilityStandards for more info. */

src/serialization/base64.hpp

@@ -15,6 +15,7 @@
 
 #pragma once
 
+#include <cstdint>
 #include <string_view>
 #include <vector>