fish_git_prompt: Use "dirty"/"staged" regex like informative

When switching this to use `git status`, I neglected to use the
correct definition of what a "dirty" and a "staged" change is.

So this now showed already staged files still as "dirty".

Fixes #8986

share/functions/fish_git_prompt.fish

@@ -269,9 +269,9 @@ function fish_git_prompt --description "Prompt function for Git"
                 test "$untracked" = true; and set opt -unormal
                 set -l stat (command git -c core.fsmonitor= status --porcelain -z --ignored=no $opt | string split0)
 
-                set dirtystate (string match -qr '^.?M' -- $stat; and echo 1)
+                set dirtystate (string match -qr '^.[ACDMR]' -- $stat; and echo 1)
                 if test -n "$sha"
-                    set stagedstate (string match -qr '^[^? ]' -- $stat; and echo 1)
+                    set stagedstate (string match -qr '^[ACDMR].' -- $stat; and echo 1)
                 else
                     set invalidstate 1
                 end

tests/checks/git.fish

@@ -85,6 +85,26 @@ fish_git_prompt
 echo
 #CHECK: (newbranch %)
 
+set -e __fish_git_prompt_showuntrackedfiles
+set -e __fish_git_prompt_status_order
+
+git -c user.email=banana@example.com -c user.name=banana commit -m foo >/dev/null
+fish_git_prompt
+echo
+#CHECK: (newbranch)
+
+echo "test" > foo
+fish_git_prompt
+echo
+#CHECK: (newbranch *)
+
+git add foo
+fish_git_prompt
+echo
+#CHECK: (newbranch +)
+
+
+
 # Turn on everything and verify we correctly ignore sus config files.
 set -g __fish_git_prompt_status_order stagedstate invalidstate dirtystate untrackedfiles stashstate
 set -g __fish_git_prompt_showdirtystate 1