[DRE-maint] Bug#912857: libruby2.5 is wrongly marked Multi-Arch: same

[Helmut Grohne]

Package: libruby2.5
Version: 2.5.1-6+b1
Severity: important
User: helmutg at debian.org
Usertags: rebootstrap

libruby2.5 is wrongly marked Multi-Arch: same. It fails to coinstall on
amd64 and arm64:

| Unpacking libruby2.5:arm64 (2.5.1-6+b1) ...
| dpkg: error processing archive /tmp/apt-dpkg-install-xsTPRC/29-libruby2.5_2.5.1-6+b1_arm64.deb (--unpack):
|  trying to overwrite shared '/usr/lib/ruby/2.5.0/rdoc/generator/template/darkfish/images/macFFBgHack.png', which is different from other instances of package libruby2.5:arm64
| dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
| Errors were encountered while processing:
|  /tmp/apt-dpkg-install-xsTPRC/29-libruby2.5_2.5.1-6+b1_arm64.deb
| E: Sub-process /usr/bin/dpkg returned an error code (1)

The multiarch hinter says:

| libruby2.5 conflicts on /usr/lib/ruby/2.5.0/rdoc/generator/template/darkfish/images/macFFBgHack.png on any two of amd64, arm64, armel, armhf, and 6 more

Please remove the erroneous Multi-Arch: same marking or fix the file
conflict.

Helmut