diffoscope: upgrade 265 -> 267

Changelog:
===========
* Use "xz --list" to supplement the output when comparing .xz archives;
  essential when some underlying metadata differs.
* 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.
* 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.
* Include "xz --verbose --verbose" (ie. double --verbose) output, not just
  the single --verbose.
* Only include "xz --list" output if the xz has no other differences.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>