zerotracepen (4.7)

Security fixes
- Upgrade Tor Browser to 9.5-build2 (Closes: #17710).
- Upgrade APT to 1.8.2.1 (DSA-4685).
- Upgrade BIND to 1:9.11.5.P4+dfsg-5.1+deb10u1 (DSA-4689).
- Upgrade WebKitGTK to 2.28.2-2~deb10u1 (DSA-4681).
- Upgrade Thunderbird to 1:68.8.0-1~deb10u1 (DSA-4683).
- Bugfixes
  - Improve Additional Software reliability (Closes: #17278): disable
    periodic APT operations entirely, adjust timeouts, force data
    synchronization, preserve file ownership.
  - Make memory erasure feature compatible with overlayfs (Closes: #15146).
  - Adjust various documentation for the new GitLab-based hosting.
- Minor improvements and updates
  - Fix title of unlock-veracrypt-volume error dialog in case of incorrect
    password (Closes: #17668).
  - Clean up confusing torrc (Closes: #17706).
- Build system
  - IUK creation: don't use extreme compression options for the outer
    SquashFS container refs.
  - IUK creation: add support for building several IUKs in parallel locally
    (Closes: #17657).
  - IUK verification: add support for fetching IUKs built in parallel on
    Jenkins (Closes: #17658).
  - Release process: generate UDFs on the alpha channel for previous
    non-final releases (Closes: #17614).
  - Remove aufs-based IUK generation code and doc (Closes: #17489).
- Test suite
  - Adjust for augmented timeouts in Additional Software.
  - Adjust locale lookup to check several directories.
  - Speed up 'I fill a ... MiB file' step by 1000%.
  - Keep latest test suite screenshot (Closes: #17621).
  - Fix test suite breaking when the user connects to the VM via virt-viewer
    (Closes: #17623).
  - Adjust reference images and titles following the migration to GitLab
    (Closes: #17718, 17719).