diffoscope fails elf tests with binutils from experimental

This bug was originally reported by Matthias Klose (doko@debian.org) in Debian bug #976760:

diffoscape fails elf test with binutils from experimental, seen on amd64:

[...]
FAILED tests/comparators/test_elf.py::test_diff - AssertionError
FAILED tests/comparators/test_elf.py::test_lib_differences - AssertionError
FAILED tests/comparators/test_elf.py::test_libmix_differences - AssertionError
============== 3 failed, 298 passed, 151 skipped in 66.22 seconds ==============
autopkgtest [17:14:17]: test pytest: -----------------------]