MDEV-35430: Add cast to semi-sync wait skip msg

This came after I prepared #3493.

sql/semisync_master.cc

@@ -939,7 +939,7 @@ int Repl_semi_sync_master::commit_trx(const char *trx_wait_binlog_name,
                 "Skipping semi-sync wait for transaction at pos %s, %lu. This "
                 "should be because semi-sync turned off and on during the "
                 "lifetime of this transaction.",
-                trx_wait_binlog_name, trx_wait_binlog_pos););
+                trx_wait_binlog_name, (unsigned long) trx_wait_binlog_pos););
 
         /* The only known reason for a missing entry at this point is if
          * semi-sync was turned off then on, so on debug builds, we track