Pin sysroot to 2.17 to ensure cpp builds are linking against correct libc

[Wumpf]

What

As indicated by the lack of pixi.lock changes, this was already the case.
Making it explicit to avoid issues when removing dependencies & to hedge against copy&paste surprises.

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Deployed docs

Commit	Link
c8d9686	https://landing-12ljnfegn-rerun.vercel.app/docs