Affected: Gitea Open Source Git Server

Fork-PR Actions task can read a third private repository via the collaborative-owner branch (missing fork-PR guard)

Affected: Go: gitea.dev

### Summary

`GetActionsUserRepoPermission` (`models/perm/access/repo_permission.go`) decides whether an Actions task token may access a target repo. Its cross-repo branches each enforce a fork-PR discriminator — **except the collaborative-owner branch**, which is missing the `!task.IsForkPullRequest` guard that its sibling has. As a result, when a private repo **B** lists owner **A** as a collaborative owner, an **attacker-controlled fork pull-request** workflow whose base repo is owned by A is granted code-read on B — i.e. the fork's YAML can clone a third private repository it has no rights to.

### Details

```go // models/perm/access/repo_permission.go (v1.26.2), in GetActionsUserRepoPermission if checkSameOwnerCrossRepoAccess(ctx, taskRepo, repo, task.IsForkPullRequest) { // passes isForkPR -> denies forks return maxPerm, nil } ... if taskRepo.IsPrivate { // <-- NO IsForkPullRequest check here actionsUnit := repo.MustGetUnit(ctx, unit.TypeActions) if actionsUnit.ActionsConfig().IsCollaborativeOwner(taskRepo.OwnerID) { return maxPerm, nil // grants code-read to target repo B } } ```

The sibling same-owner path correctly denies fork PRs:

```go func checkSameOwnerCrossRepoAccess(ctx, taskRepo, targetRepo, isForkPR bool) bool { if isForkPR { return false // Fork PRs are never allowed cross-repo access to other private repositories. } ... } ```

`taskRepo` = the repo…