Upgrade to pnpm v8

[andrewiggins]

It appears some of our Netlify builds (e.g. in PR #375) are failing due to pnpm version mismatch. This PR upgrades our version to the latest (v8) to fix them.

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Latest commit: 5db8414

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[andrewiggins]

Note - compressed-size action will fail cuz it checks out the previous main branch which has the old lockfile and isn't compatible with the new lock file

[JoviDeCroock]

Merged it as it fixes our workflows for other PR's