Adapt Github action rules to avoid Node16 and upgrade to Node20

[sarroutbi]

Some warnings are being dumped in Github Actions. Examples:

This is due to usage of Node16 based Github actions. Versions should be upgraded (for example, checkout from v3 to v4).
More information here:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/

At least, next Github actions are affected:

.github/workflows/build.yml:      - uses: actions/checkout@v3
.github/workflows/differential-shellcheck.yml:        uses: actions/checkout@v3
.github/workflows/spellcheck.yml:        uses: actions/checkout@v3