cargo: bump gix-actor to v0.31.4

Gitoxide, which is used to parse git commits, previously failed to parse
some malformed author/committer lines.

In 0.31.4, this parsing was made more lenient so as to better match
Git's parsing and avoid breaking on "in-the-wild" repositories such as
https://github.com/LibreOffice/core

Refs: GitoxideLabs/gitoxide#1438
Fixes: #4008