CaiCandong c576b50441 Fix being unable to use a repo that prohibits accepting PRs as a PR source. (#26785) ... ## Description Sometimes, we need to use an upstream mirror repository to update the current development repository, but mirror repositories are prohibited from PR. It should not appear in `merge to,` but it can appear in `pull from.` Fix #24585 #26193 #26781 Related #24183 Many thanks to @apnote for assisting me in reproducing this bug! ## ScreenShot --- ### Before <img src="https://github.com/go-gitea/gitea/assets/50507092/3d76c376-1f54-45b9-80c9-6ba8319d6a9a" width="400px"> <img src="https://github.com/go-gitea/gitea/assets/50507092/fbfd9f7f-421f-4a2e-9a3e-f2958bbf3312" width="400px"> ### After <img src="https://github.com/go-gitea/gitea/assets/50507092/e6984524-4f61-4310-b795-4d8598bd8963" width="400px"> <img src="https://github.com/go-gitea/gitea/assets/50507092/04065b44-78d7-4721-bf31-0f1674150727" width="400px">		2023-08-29 12:07:15 +03:00
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