win32: do not test for ctime difference

ctime is file creation time on windows and is not updated on "touch".

src/borg/testsuite/archiver/diff_cmd_test.py

@@ -173,7 +173,7 @@ def get_changes(filename, data):
         unexpected = {"type": "modified", "added": 0, "removed": 0}
         assert unexpected not in get_changes("input/file_touched", joutput)
         if not content_only:
-            assert {"ctime", "mtime"}.issubset({c["type"] for c in get_changes("input/file_touched", joutput)})
+            assert {"mtime"}.issubset({c["type"] for c in get_changes("input/file_touched", joutput)})
         else:
             # And if we're doing content-only, don't show the file at all.
             assert not any(get_changes("input/file_touched", joutput))