chore(generate): update termux-pacman mirror and bootstrap version format

[robertkirkman]

• After this PR chore(ci): synchronize with upstream termux-apt termux-pacman/termux-packages#402 the termux-pacman bootstrap version format now has a . symbol instead of the second - symbol, which has been done in order to make the format match that which termux-apt has had since termux/termux-packages@83dc034, so termux-docker needs to be updated to match, otherwise an error will occur if the bootstrap version is bumped without updating the format.

• Bump both bootstrap versions at the same time to 2026.04.26, for consistency.

• Update to new termux-pacman mirror sync.termux-pacman.dev after this PR, since service.termux-pacman.dev is currently down: chore(main/pacman): add backup mirror sync.termux-pacman.dev termux-packages#29464

[robertkirkman]

@sylirre I am just pinging you to let you know that I plan to merge this PR myself after a little while, since it seems to me to be minor and necessary maintenance changes that are fully validated by the CI passing, and also this will fix the CI that failed yesterday because of the termux-pacman mirror being down, https://github.com/termux/termux-docker/actions/runs/24946802464 and also after that is fixed, the next termux-docker-pacman image will have the updated mirror in its mirrorlist, so it will be easier to select it at runtime.

but if you prefer me to wait for review from you before merging this kind of PR myself, let me know and then I wouldn't merge it without review.