audit-type: include alloc-util.h for newa() (#40389)

The macro audit_type_name_alloca() needs newa() which is defined in
alloc-util.h.

src/libsystemd/sd-journal/audit-type.h

@@ -5,6 +5,8 @@
 
 #include "sd-forward.h"
 
+#include "alloc-util.h" /* IWYU pragma: keep */
+
 DECLARE_STRING_TABLE_LOOKUP(audit_type, int);
 
 /* This is inspired by DNS TYPEnnn formatting */