Let `MinUnitAccessMode` return correct perm (#18675)
Let `MinUnitAccessMode` return correct perm (#18675)

- Don't let `TypeExternalTracker` or `TypeExternalWiki` influence the
minimal permission, as they won't be higher than read. So even if all
the other ones are write, these 2 will ensure that's not higher than
read.
- Partially resolves #18572 (Point 1,2,5?)

Co-authored-by: zeripath <6a547fdd28db89120bdd70d4af1f9ba672ccd43a@cantab.net>
go-gitea/gitea,go-gitea/gitea,go-gitea/gitea