Add ONLY_SHOW_RELEVANT_REPOS back, fix explore page bug, make code more strict (#23766)#23791

jolheiser merged 3 commits intogo-gitea:release/v1.19go-gitea/gitea:release/v1.19from

wxiaoguang:fix-explore-repo-backportwxiaoguang/gitea:fix-explore-repo-backportCopy head branch name to clipboard