Recovery with innodb_log_recovery_target wrongly opens log in read-write mode

During the development of MDEV-14992, the test backup.backup_innodb failed on Microsoft Windows due to ERROR_ACCESS_DENIED. It appears that the write permission on a log file is being revoked while the server is starting up. A premature mariadbd process startup is probably an issue with the regression test driver itself (see MDEV-28976).

In any case, there is no reason to open the log files in read/write mode when innodb_log_recovery_target is set. In this mode, we are only supposed to recover the data files based on the log file contents, and not allow any writes from applications or to the log.