GH Actions: version update for various predefined actions

[jrfnl]

A number of predefined actions have had major release, which warrant an update to the workflow(s).

These updates don't actually contain any changed functionality, they are mostly just a change of the Node version used by the action itself (from Node 14 to Node 16).

Refs:

• https://github.com/actions/checkout/releases

[jrfnl]

Hmm.. the build failure looks unrelated to this PR.

[jaapio]

Thanks, also here, dependabot will handle this :-)

[jrfnl]

@jaapio Yup, no worries, I've scrapped them off my list and am actually looking to add dependabot for specifically these action runners to various repos.