fish_git_prompt: fix buggy rename parsing

Commit f86c9af455 (fish_git_prompt: skip rename/copy source paths in
status parsing, 2026-05-12).  filters from "git-status --porcelain"
output all lines that don't look like a status entry.  This is
to filter out the rename source path.  But the filtering has false
positives, e.g. if a rename source path starts with "AA".  Let's only
skip lines immediately after each rename entry.  Also for copy (C)
though I haven't found a test case for that yet.

share/functions/fish_git_prompt.fish

@@ -408,9 +408,17 @@ end
 ### helper functions
 
 function __fish_git_prompt_status_porcelain_modulo_rename_source
-    git -c core.fsmonitor= status --porcelain -z $argv |
-        string split0 |
-        string match -r '^[ MADRCTU?!]{2} .*'
+    set -l skip false
+    for line in (git -c core.fsmonitor= status --porcelain -z $argv | string split0)
+        if $skip
+            set skip false
+            continue
+        end
+        printf %s\n $line
+        if string match -rq -- ^[RC] $line
+            set skip true
+        end
+    end
 end
 
 function __fish_git_prompt_informative_status