Fix git_prompt_status() not showing ahead/behind/diverged status correctly (#5388)

lib/git.zsh

@@ -165,13 +165,13 @@ function git_prompt_status() {
   if $(echo "$INDEX" | grep '^UU ' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_UNMERGED$STATUS"
   fi
-  if $(echo "$INDEX" | grep '^## .*ahead' &> /dev/null); then
+  if $(echo "$INDEX" | grep '^## [^ ]\+ .*ahead' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_AHEAD$STATUS"
   fi
-  if $(echo "$INDEX" | grep '^## .*behind' &> /dev/null); then
+  if $(echo "$INDEX" | grep '^## [^ ]\+ .*behind' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_BEHIND$STATUS"
   fi
-  if $(echo "$INDEX" | grep '^## .*diverged' &> /dev/null); then
+  if $(echo "$INDEX" | grep '^## [^ ]\+ .*diverged' &> /dev/null); then
     STATUS="$ZSH_THEME_GIT_PROMPT_DIVERGED$STATUS"
   fi
   echo $STATUS