zsh:git-commit-last-msg(): Support additional args

Pass additional arguments to git-commit so that flags can be passed
e.g `-n` to bypass the commit hooks.
Also use the according completion for `git-commit-last-msg`.

.config/zsh/zshrc.d/20-completion.zsh

@@ -38,6 +38,7 @@ compdef nvim-man=man
 # Copy git completion for arguments
 compdef _git-log glog
 compdef _git-checkout git-checkout-worktree
+compdef _git-commit git-commit-last-msg
 # Run git's completion once to avoid a `command not found` error when using the
 # completion functions on other programs without having completed something for
 # git before in the same session.