fix(git): avoid "illegal byte sequence" in prompt status regex

Closes #13330

When `git status --porcelain` output contains an invalid byte sequence
(e.g. a filename that is not valid UTF-8 under the current locale), zsh's
`=~` regex operator delegates to the C library `regexec`, which aborts with
REG_ILLSEQ and prints "regex matching error: illegal byte sequence". This
happens once for every status prefix in `_omz_git_prompt_status`, polluting
the prompt with repeated error messages and causing all per-file statuses to
be lost.

Force the C locale inside the function with `local -x LC_ALL=C`. In the C
locale every byte is a valid single-byte character, so the regex matching
never fails that way. `git status --porcelain` is locale-independent, so the
parsed output is unchanged.

Verification: `zsh -n lib/git.zsh` passes and the full CI syntax check loop
(`zsh -n` on 576 scripts) reports zero failures.

lib/git.zsh

@@ -40,6 +40,15 @@ function _omz_git_prompt_info() {
 }
 
 function _omz_git_prompt_status() {
+  # OHMYZSH-13330: avoid "regex matching error: illegal byte sequence".
+  # zsh's "=~" operator delegates to the C library regex, which aborts with
+  # REG_ILLSEQ when the subject contains an invalid byte sequence under a
+  # multibyte locale (e.g. a filename with non-UTF-8 bytes in `git status`
+  # output). Forcing the C locale makes every byte a valid character, so the
+  # regex matching below never fails that way. `git status --porcelain` is
+  # locale-independent, so this does not change the parsed output.
+  local -x LC_ALL=C
+
   [[ "$(__git_prompt_git config --get oh-my-zsh.hide-status 2>/dev/null)" = 1 ]] && return
 
   # Maps a git status prefix to an internal constant