Misc: Use [[fallthrough]] attribute instead of comment to mark intentional fallthroughs (#25054)

Related: #25006
(cherry picked from commit 85b5b842ca6c05d4e51081e6c3282940a80f3761)

src/server/database/Database/MySQLConnection.cpp

@@ -545,8 +545,8 @@ bool MySQLConnection::_HandleMySQLErrno(uint32 errNo, uint8 attempts /*= 5*/)
                 mysql_close(m_Mysql);
                 m_Mysql = nullptr;
             }
+            [[fallthrough]];
         }
-        /* fallthrough */
         case CR_CONN_HOST_ERROR:
         {
             TC_LOG_INFO("sql.sql", "Attempting to reconnect to the MySQL server...");