libaec: update project URLs and SHA256 hash

[adamzap]

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• Is your test running fine brew test <formula>?
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• I did not use AI/LLM to create this PR, or I disclosed the tool/model below and reviewed its output; I did not attribute commits to AI and will answer maintainer questions and review comments myself without AI/LLM.

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GitHub seems to be the authoritative home of this project now. The SHA256 hash changed because GitHub provides a .tar.gz file rather than a .tar.bz2 file, and the new archive contains more files.

I'm not an authority on this project. I'm just trying to fix the formula so that I can build the library locally via Homebrew. When building on main, I have consistently gotten the following error over multiple days:

Download failed: https://gitlab.dkrz.de/k202009/libaec/-/archive/v1.1.7/libaec-v1.1.7.tar.bz2
curl: (56) The requested URL returned error: 429