Pin node version to v16. Fix #135

[sunoru]

Run the builds with Node v16 since v18 is the default on github action runners now (actions/runner-images#7002). It will fix #135.

We can remove these lines whenever using: node18 is available: https://docs.github.com/en/actions/creating-actions/metadata-syntax-for-github-actions#runsusing-for-javascript-actions

[DilumAluthge]

What about users of this action? Do they need to do something to make sure that when they use the setup-julia action, that Node 16 will be used?

[sunoru]

No, they won't be affected at all. setup-julia always uses node v16 in users' actions as defined here

The issue of github defaulting to node v18 only caused our "Example builds" under this repo to fail.

[SaschaMann]

Thank you