Use safer append to hook function arrays (#8406)

Use add-zsh-hook to add functions to hooks. That way they won't be added again
when doing `source ~/.zshrc` multiple times.

Co-authored-by: Marc Cornellà <marc.cornella@live.com>

plugins/dirhistory/dirhistory.plugin.zsh

@@ -53,7 +53,8 @@ function push_future() {
 }
 
 # Called by zsh when directory changes
-chpwd_functions+=(chpwd_dirhistory)
+autoload -U add-zsh-hook
+add-zsh-hook chpwd chpwd_dirhistory
 function chpwd_dirhistory() {
   push_past $PWD
   # If DIRHISTORY_CD is not set...