completion: zsh: stop leaking local cache variable

Completing commands like "git rebase" in one repository will leak the local __git_repo_path into the shell's environment so that completing commands after changing to a different repository will give the old repository's references (or none at all). The bug report on the mailing list [1] suggests one simple way to observe this yourself: Enter the following commands from some directory: mkdir a b b/c for d (a b); git -C $d init && git -C $d commit --allow-empty -m init cd a git branch foo pushd ../b/c git branch bar Now type these: git rebase <TAB>… # completion for bar available; C-c to abort declare -p __git_repo_path # outputs /path/to/b/.git popd git branch # outputs foo, main git rebase <TAB>… # completion candidates are bar, main! Ideally, the last typed <TAB> should be yielding foo, main. Commit beb6ee7163 (completion: extract repository discovery from __gitdir(), 2017-02-03) anticipated this problem by marking __git_repo_path as local in __git_main and __gitk_main for Bash completion but did not give the same mark to _git for Zsh completion. Thus make __git_repo_path local for Zsh completion, too. [1]: https://lore.kernel.org/git/CALnO6CBv3+e2WL6n6Mh7ZZHCX2Ni8GpvM4a-bQYxNqjmgZdwdg@mail.gmail.com/ Signed-off-by: D. Ben Knoble <ben.knoble+github@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>