Announce: flatpak 1.12.6

[Phaedrus Leeds]

Available at:
  https://github.com/flatpak/flatpak/releases/tag/1.12.6

$ sha256sum flatpak-1.12.6.tar.xz
ef02cb505b91cce5173099b5485768eef1899ebcf39edf827c4254163a811627  flatpak-1.12.6.tar.xz

* Fix a bug that sometimes caused repo corruption in case downloads are
  interrupted or canceled, necessitating a "flatpak repair" to recover
  (#3479, #4258)
* More reliably detect the GTK theme (#4754)
* Fix history command unit test in some edge cases (#4764)
* Improve NEWS for 1.12.5
* Translation update: pt_BR