👷 Use ballerina action for setup

[homersimpsons]

Fixes #204

[github-actions]

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[homersimpsons]

@BNAndras Thank you for the approval. Note that I cannot merge on this repository (I do not really intend to contribute more here, so no need to give me the right). Can you merge it as well?

Also there are 2 commits, I believe the default setting is to squash them, but if not you should be able to squash them from the UI. If you cannot I will do it manually (but I have to open a GitHub Codespace for this).

[BNAndras]

I’m a cross-track reviewer, not a Ballerina maintainer so I’ll defer to them for the final approval / merge.