Bug#946854: s390x/ppc builds are failing in the newest version

[Sebastien Bacher]

Package: dulwhich
Version: 0.19.14-2

The build/tests are failing on s390x and ppc,
https://buildd.debian.org/status/fetch.php?pkg=dulwich&arch=s390x&ver=0.19.14-2&stamp=1576422406&raw=0

0.19.13 was building fine on those architectures