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 for updating these :-)

[jrfnl]

@jaapio Just checking as you remarked on one of the other PRs that this is normally handled via Dependabot - can I take all the phpDocumentor organisation repos of my list of typical repos I'd send these type of updates to ?

[jaapio]

yes, you can. we let Dependabot do this :-)