Fix Permission in API returned repository struct (#25388)

The old code generates `structs.Repository.Permissions` with only
`access.Permission.AccessMode`, however, it should check the units too,
or the value could be incorrect. For example,
`structs.Repository.Permissions.Push` could be false even the doer has
write access to code unit.

Should fix
https://github.com/renovatebot/renovate/issues/14059#issuecomment-1047961128
(Not reported by it, I just found it when I was looking into this bug)

---

Review tips:

The major changes are
- `modules/structs/repo.go`
https://github.com/go-gitea/gitea/pull/25388/files#diff-870406f6857117f8b03611c43fca0ab9ed6d6e76a2d0069a7c1f17e8fa9092f7
- `services/convert/repository.go`
https://github.com/go-gitea/gitea/pull/25388/files#diff-7736f6d2ae894c9edb7729a80ab89aa183b888a26a811a0c1fdebd18726a7101

And other changes are passive.

services/convert/notification.go

@@ -9,6 +9,7 @@ import (
 	activities_model "code.gitea.io/gitea/models/activities"
 	"code.gitea.io/gitea/models/db"
 	"code.gitea.io/gitea/models/perm"
+	access_model "code.gitea.io/gitea/models/perm/access"
 	api "code.gitea.io/gitea/modules/structs"
 )
 
@@ -24,7 +25,7 @@ func ToNotificationThread(n *activities_model.Notification) *api.NotificationThr
 
 	// since user only get notifications when he has access to use minimal access mode
 	if n.Repository != nil {
-		result.Repository = ToRepo(db.DefaultContext, n.Repository, perm.AccessModeRead)
+		result.Repository = ToRepo(db.DefaultContext, n.Repository, access_model.Permission{AccessMode: perm.AccessModeRead})
 
 		// This permission is not correct and we should not be reporting it
 		for repository := result.Repository; repository != nil; repository = repository.Parent {