git: use is-at-least to test for git version

Fixes #7754

plugins/git/git.plugin.zsh

@@ -241,7 +241,8 @@ alias gss='git status -s'
 alias gst='git status'
 
 # use the default stash push on git 2.13 and newer
-[[ "$(git --version 2>/dev/null)" =~ '^git version ([0-9]+.[0-9]+)' && "$match" -ge '2.13' ]] \
+autoload -Uz is-at-least
+is-at-least 2.13 "$(git --version 2>/dev/null | awk '{print $3}')" \
   && alias gsta='git stash push' \
   || alias gsta='git stash save'