Gitea private pull request disclosure on project boards

Repository and organization project boards listed the pull requests that reference each issue on the board without checking whether the viewer can read them. When a private pull request mentions an issue on a board the viewer can open, the board revealed the private repository's path and the pull request's number, title and state, to anonymous visitors in the case of a public board. The pull request body, diff and files were not exposed. Boards now skip linked pull requests in repositories where the viewer cannot read pull requests.