dpkg: upgrade 1.21.7 -> 1.21.8

dpkg: upgrade 1.21.7 -> 1.21.8

Changelog:
==========
  * dpkg-statoverride: Add support for --force-not-root. Closes: #1009069
  * dpkg: Fix <De-configuring> message to allow configuration to use new
    version.
  * Perl modules:
    - Dpkg::Source::Archive: Prevent directory traversal for in-place extracts.
    - Dpkg::Substvars: Add support for optional substvars assigned with ?=.
  * Documentation:
    - man: Reference deb-substvar(5) from dpkg-source(1) and dpkg-shlibdeps(1).
    - man: Structure and clarify deb-substvars(5).
  * Build system:
    - Unhook dist-cpan from make dist target.
  * Packaging:
    - Silence warning about merged-usr-via-aliased-dirs on Ubuntu.
    - Remove useless [] around tr sets.
  * Localization:
    - Update Dutch translations. Closes: #1010031, #1010032, #1010033
    - Update Portuguese man pages translations. Closes: #1011095
  * Localization:
    - Update German man pages translation.

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>