Fix new gcc errors for missing types.

Errors when building with gcc 13:
ranked_match.hh:10:21: error: ‘uint64_t’ does not name a type
   10 | using UsedLetters = uint64_t;
      |                     ^~~~~~~~

src/keys.hh

@@ -9,6 +9,8 @@
 #include "unicode.hh"
 #include "vector.hh"
 
+#include <cstdint>
+
 namespace Kakoune
 {
 

src/ranked_match.hh

@@ -4,6 +4,8 @@
 #include "string.hh"
 #include "meta.hh"
 
+#include <cstdint>
+
 namespace Kakoune
 {