knot: update to version 3.5.6

[Payne-X6]

📦 Package Details

Maintainer: @salzmdan

Description:

• Release notes: https://www.knot-dns.cz/2026-07-20-version-356.html

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🧪 Run Testing Details

• OpenWrt Version: TurrisOS 9.2.0
• OpenWrt Target/Subtarget: mvebu/cortexa9
• OpenWrt Device: Turris Omnia

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✅ Formalities

• I have reviewed the CONTRIBUTING.md file for detailed contributing guidelines.

If your PR contains a patch:

• It can be applied using git am
• It has been refreshed to avoid offsets, fuzzes, etc., using

  make package/<your-package>/refresh V=s

• It is structured in a way that it is potentially upstreamable
  _{(e.g., subject line, commit description, etc.)
  We must try to upstream patches to reduce maintenance burden.}