test(file-ops): make the unicode-variant retry test filesystem-independent

Follow-up to the salvaged #95160. The test wrote the NFC spelling of
café.txt and read the NFD spelling. APFS resolves NFD lookups to the NFC
file directly, so on macOS the compound probe simply found the file, the
retry path never ran and r.hint was None -> TypeError (Linux CI passed
because ext4 does not alias normalisation forms).

Use a curly-vs-ASCII apostrophe instead: still visually identical, still
mapped by _unicode_variant_match, and never aliased by any filesystem, so
the retry path is exercised everywhere.

tests/tools/test_file_ops_single_roundtrip.py

@@ -11,7 +11,6 @@ import logging
 import os
 import sys
 import threading
-import unicodedata
 from unittest.mock import patch
 
 import pytest
@@ -160,13 +159,17 @@ class TestReadFileNonTextPaths:
 
     def test_unicode_variant_retry_still_works(self, shell, tmp_path):
         ops, calls = shell
-        nfc = unicodedata.normalize("NFC", "café.txt")
-        nfd = unicodedata.normalize("NFD", "café.txt")
-        assert nfc != nfd
-        _write(tmp_path, nfc, b"accent\n")
-        r = ops.read_file(str(tmp_path / nfd))
+        # A curly apostrophe vs the ASCII one: visually identical in a
+        # terminal, and — unlike NFC/NFD — never aliased by the filesystem
+        # (APFS resolves NFD lookups to NFC files directly, which would skip
+        # the retry path this test exists to exercise).
+        on_disk = "it\u2019s.txt"
+        typed = "it's.txt"
+        assert on_disk != typed
+        _write(tmp_path, on_disk, b"accent\n")
+        r = ops.read_file(str(tmp_path / typed))
         assert r.error is None and r.content == "1|accent\n2|"
-        assert "unicode-equivalent" in r.hint
+        assert r.hint is not None and "unicode-equivalent" in r.hint
 
     def test_directory_is_not_regular(self, shell, tmp_path):
         ops, calls = shell