Fix owner team access mode value in team_unit table (#23675)

Fix owner team access mode value in team_unit table (#23675)

All `access_mode` value of Owner Teams are 0(AccessModeNone) in
`team_unit` table, which should be 4(AccessModeOwner)
In `team` table:

![image](https://user-images.githubusercontent.com/18380374/227409457-1b9660ae-8cf7-49c8-a013-1850b46baebc.png)
In `team_unit` table:

![image](https://user-images.githubusercontent.com/18380374/227409429-a793dd90-4ae1-4191-b95b-e288c591f9fd.png)

ps: In https://github.com/go-gitea/gitea/pull/23630, `access_mode` in
`team_unit` is used to check the team unit permission, but I found that
user can not see issues in owned org repos.