packaging: update dulwich to drop the certifi dependency on Windows

The presence of certifi causes the system certificate store to be ignored, which was reported as a bug against TortoiseHg[1]. It was only pulled in on Windows because of dulwich, which was copied from the old TortoiseHg install scripts, in order to support hg-git.

This version of dulwich raises the minimum urllib3 to a version (1.25) that does certificate verification by default, without the help of certifi[2]. We already bundle a newer version of urllib3. Note that certifi can still be imported from the user site directory, if installed there. But the installer no longer disables the system certificates by default.

[1] mercurial/tortoisehg/thg#5825 (closed) [2] https://github.com/jelmer/dulwich/issues/1025