bug#18640: fontconfig's cache is not refreshed automatically

[宋文武]

Hello, I believe this issue had been fixed by:

commit 6f12880a76a6c91058718d15845f8b9d9b529a5a
Author: Sarah Morgensen <iskarian@mgsn.dev>
Date:   Fri Jun 18 17:52:05 2021 -0700

    gnu: fontconfig: Use (locally) deterministic caching
    
    Make fontconfig use directory contents rather than modification time to
    determine cache validity (by pretending that mtime is broken).

Closing.