git: Move git-bug completion sourcing to correct shell

vcs/git/config/sh/alias.d/git-bug.sh

@@ -4,10 +4,6 @@ if ! exist git-bug; then
     return 1
 fi
 
-# POSIX-compliant version of . <(cmd) substitution
-# shellcheck source=/dev/null # but shellcheck can't access
-git-bug completion zsh | . /dev/fd/0
-
 alias gbt='git-bug termui'
 gb() {
     if [ "$#" -eq 1 ] && git-bug bug status "$1" >/dev/null 2>/dev/null; then

vcs/git/config/zsh/alias.d/git-bug-completions.zsh

@@ -0,0 +1,7 @@
+#!/usr/bin/env zsh
+
+if ! exist git-bug; then
+    return 1
+fi
+
+source <(git-bug completion zsh)