(MODULES-11374) Update GitHub Action Ubuntu runner

(MODULES-11374) Update GitHub Action Ubuntu runner

GitHub is deprecating Ubuntu 18.04 runners on April 1, 2023. This
commit switches all Ubuntu 18.04 runners used in GitHub Actions to
Ubuntu 20.04.

https://github.blog/changelog/2022-08-09-github-actions-the-ubuntu-18-04-actions-runner-image-is-being-deprecated-and-will-be-removed-by-12-1-22/

This commit also updates all instances of the actions/checkout@v2
to actions/checkout@v3 in perparation for the former's deprecation
as part of the NodeJS deprecation.

https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/