[Packaging] Add support for Debian forky

[kou]

Describe the enhancement requested

Debian trixie released on 2025-08-09: https://www.debian.org/News/2025/20250809

The next testing is forky. Let's add support for it.

Component(s)

Packaging

[kou]

Oh, we already have Debian trixie support.

Let's reuse this for the next testing, Debian forky.

[kou]

Issue resolved by pull request 47342
#47342