py-diffoscope: update to version 266

Changelog:

Version 266 includes the following changes:

[ Chris Lamb ]
* Use "xz --list" to supplement the output when comparing .xz archives;
essential when some underlying metadata differs. (Closes: #1069329)
* Actually append the xz --list after the container differences, as it
simplifies tests and the output.
* Add 7zip to <!nocheck> Build-Depends in debian/control.
* Update copyright years.

[ James Addison ]
* Maintain an in-header boolean state to determine whether to drop
from-file/to-file lines. This fixes an issue where HTML differences were
being inadvertendly neglected. (Closes: reproducible-builds/diffoscope#372)

Version 265 includes the following changes:

[ Chris Lamb ]
* Ensure that tests with ">=" version constraints actually print the
corresponding tool name. (Closes: reproducible-builds/diffoscope#370)
* Prevent odt2txt tests from always being skipped due to an impossibly new
version requirement. (Closes: reproducible-builds/diffoscope#369)
* Avoid nested parens-in-parens when printing "skipping…" messages
in the testsuite.

(nikita)