Bug#985492: python-debian: should include Build-Depends-Arch and Build-Conflicts-Arch

[Yangfl]

Package: python-debian
Severity: important

https://salsa.debian.org/python-debian-team/python-debian/-/blob/master/lib/debian/deb822.py#L2274

which ignores Build-Depends-Arch and Build-Conflicts-Arch as mentioned in

https://www.debian.org/doc/debian-policy/ch-relationships.html#relationships-between-source-and-binary-packages-build-depends-build-depends-indep-build-depends-arch-build-conflicts-build-conflicts-indep-build-conflicts-arch