Git hooks don't run while commiting in worktree via git-gui

Hello. There is a little difference in behavior when you are committing to the worktree from CLI or some git client (tortoisegit/sourcetree) and embedded git gui.

If you configure git hooks in your repository and then add a worktree (via git worktree add), hooks from main repository works well both in main directory and in worktree, if you are using CLI/third-party GUI. Committing in the main directory via embedded git-gui works fine too, hooks are running. But when you try to commit in the worktree directory from git-gui, hooks don't work.

I think I've found the cause of this: https://github.com/git/git/blob/master/git-gui/lib/commit.tcl#L238 variable fd equals {} because proc githook_read calls proc gitdir to determine path to hooks. https://github.com/git/git/blob/master/git-gui/git-gui.sh#L626 This proc use variable _gitdir for calculating result. This var equals the result of executing git rev-parse --git-dir https://github.com/git/git/blob/master/git-gui/git-gui.sh#L1245 So, the path to hooks for worktree is path_to_main_repo/.git/worktrees/my_worktree/hooks, but there are no hooks. Hooks are in path_to_main_repo/.git/hooks, from where they are correctly (or not?) executed by git cli, while running from worktree directory.

If we put hooks to path_to_main_repo/.git/worktrees/my_worktree/hooks too, they will work both in git citool and CLI/third-party GUI. But they will execute different files, and it may cause some problems.