ci(fix): pin cspell to v9, they changed the syntax and broke it

[braindigitalis]

This has been broken a couple of months, pin it to v9 so it stops erroring and we can finally get green CI.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

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