Update Node version for flaky test reporter

[Mamaduka]

What?

PR updates the Node version for the flaky test reporter action.

Why?

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.

Testing Instructions

It shouldn't generate a notice in the e2e tests summary.

[github-actions]

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[Mamaduka]

@kevin940726, are there other places I need to update the Node version for this action? Because the notice is still displayed - https://github.com/WordPress/gutenberg/actions/runs/9413245504?pr=62401

[kevin940726]

Thanks!

[kevin940726]

@kevin940726, are there other places I need to update the Node version for this action? Because the notice is still displayed - https://github.com/WordPress/gutenberg/actions/runs/9413245504?pr=62401

Because it checkouts to trunk to run the action. I believe the warning will go away once we merge this to trunk!