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.

routers/api/v1/repo/fork.go

@@ -60,12 +60,12 @@ func ListForks(ctx *context.APIContext) {
 	}
 	apiForks := make([]*api.Repository, len(forks))
 	for i, fork := range forks {
-		access, err := access_model.AccessLevel(ctx, ctx.Doer, fork)
+		permission, err := access_model.GetUserRepoPermission(ctx, fork, ctx.Doer)
 		if err != nil {
-			ctx.Error(http.StatusInternalServerError, "AccessLevel", err)
+			ctx.Error(http.StatusInternalServerError, "GetUserRepoPermission", err)
 			return
 		}
-		apiForks[i] = convert.ToRepo(ctx, fork, access)
+		apiForks[i] = convert.ToRepo(ctx, fork, permission)
 	}
 
 	ctx.SetTotalCountHeader(int64(ctx.Repo.Repository.NumForks))
@@ -152,5 +152,5 @@ func CreateFork(ctx *context.APIContext) {
 	}
 
 	// TODO change back to 201
-	ctx.JSON(http.StatusAccepted, convert.ToRepo(ctx, fork, perm.AccessModeOwner))
+	ctx.JSON(http.StatusAccepted, convert.ToRepo(ctx, fork, access_model.Permission{AccessMode: perm.AccessModeOwner}))
 }