minor #444 Update GitHub Actions workflow to actions/checkout@v4 (TimWolla)

This PR was squashed before being merged into the 1.x branch.

Discussion
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Update GitHub Actions workflow to `actions/checkout@v4`

This fixes the following deprecation:

> The following actions uses node12 which is deprecated and will be forced to
> run on node16: actions/checkout@v2. For more info:
> https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/

Commits
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ba52ff0 Update GitHub Actions workflow to `actions/checkout@v4`

Author: derrabus

.github/workflows/tests.yml

@@ -29,7 +29,7 @@ jobs:
 
         steps:
             -   name: Checkout
-                uses: actions/checkout@v2
+                uses: actions/checkout@v4
 
             -   name: Setup PHP
                 uses: shivammathur/setup-php@v2