GH Actions: version update for various actions (3.x branch)

[jrfnl]

GH Actions: version update for various predefined actions

A number of predefined actions have had major releases, 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

GH Actions: version update for actions/cache

This major and the subsequent releases does have functional changes, but none AFAICS which impact the workflow.

Ref: https://github.com/actions/cache/releases

[codecov[bot]]

Codecov Report

Merging #44 (aea1e63) into 3.1 (0c32ea2) will not change coverage. The diff coverage is n/a.

:exclamation: Current head aea1e63 differs from pull request most recent head ec9b104. Consider uploading reports for the commit ec9b104 to get more accurate results

@@            Coverage Diff            @@
##                3.1      #44   +/-   ##
=========================================
  Coverage     96.03%   96.03%           
  Complexity       55       55           
=========================================
  Files             1        1           
  Lines           126      126           
=========================================
  Hits            121      121           
  Misses            5        5           

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[jrfnl]

Added an extra commit with the COMPOSER_ROOT_VERSION fix, which I already previously applied to the 4.x branch in #37