GH Actions: version update for actions/cache (#224)

A number of predefined actions have had major releases, which warrant an update.

The update doesn't actually contain any changed functionality, it's mostly just a change of the Node version used by the action itself (from Node 12 to Node 16), but see the changelog for more info.

Refs:
* https://github.com/actions/cache/releases/

Co-authored-by: jrfnl <jrfnl@users.noreply.github.com>

action.yml

@@ -70,7 +70,7 @@ runs:
 
     - name: "Cache Composer dependencies"
       if: steps.should-cache.outputs.do-cache == 1
-      uses: "actions/cache@v2"
+      uses: "actions/cache@v3"
       with:
         path: "${{ steps.composer.outputs.cache-dir }}"
         key: "${{ steps.cache-key.outputs.key }}"