Bump Haddock GHC to 9.6.7

[martijnbastiaan]

Our current documentation's Javascript on Hackage is broken, making it hard to navigate. This has been solved in newer GHCs.

Fixes #2981

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We shouldn't merge the backport of this PR, before we've seen a nightly run publish to Hackage and checking the documentation for obvious flaws.

Still TODO:

• Write a changelog entry (see changelog/README.md)
• Check copyright notices are up to date in edited files

[DigitalBrains1]

Leon and I spent some brain cycles on this as well.

It's probably better to use GHC 9.6 until GHC MR 14447 has made it to a version of GHC we support in Clash. Because I think our CI job is going to really balk at all the link destination warnings.

Leon and I were also discussing ways to diff the before and after of our Haddock, and reducing that diff to something a human can grok, to check if stuff broke. Because I'm worried updating to a newer Haddock will break stuff, either because we did something wrong that caused no issue before but now does, or because Haddock changed something in a way that doesn't work how we use it (like the Cabal upgrade did recently).

[martijnbastiaan]

Alright, I'll change it to 9.6. I'll report an issue so we don't forget to diff. I do think moving forward on this (even if it breaks some other things) is the way to go, because of how massively broken the status quo is.