Revert "Update cache action runner (#252)"

This reverts commit 0b4a7fe.

This avoids any potential backwards-compatibility issues that might
arise when using self-hosted runners that use Node.js 16 instead of
version 20.

For more details, see the discussion here:
#252

action.yml

@@ -80,7 +80,7 @@ runs:
 
     - name: "Cache Composer dependencies"
       if: steps.should-cache.outputs.do-cache == 1
-      uses: "actions/cache@v4"
+      uses: "actions/cache@v3"
       with:
         path: "${{ steps.composer.outputs.cache-dir }}"
         key: "${{ steps.cache-key.outputs.key }}"