Update CI to actions/checkout@v4

alsa-project/alsa-lib issue #389 was opened from ryandesign:

As it says in the annotations of recent CI builds:

Node.js 16 actions are deprecated. Please update the following actions to use Node.js 20: actions/checkout@v3. For more information see: https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-n....

In other words, switch to actions/checkout@v4.

Issue URL : https://github.com/alsa-project/alsa-lib/issues/389 Repository URL: https://github.com/alsa-project/alsa-lib