CVE-2026-47712 Dulwich doesn't sanitize commit subjects in `porcelain.format_patch`

Dulwich is a pure-Python implementation of the Git file formats and protocols. Starting in version 0.24.0 and prior to version 1.2.5, dulwich.porcelain.formatpatchoutdir=... derives each patch filename from the commit's subject line. Prior to this fix, getsummary only replaced spaces with dashes ...