Update actions checkout/cache/upload-artifact to v3 and update Ubuntu runners

[mcanouil]

This PR updates the following actions in various places (it's recommended to switch to v3 at least for checkout and cache actions):

• checkout from v2 to v3: released in march 2022 (https://github.com/actions/checkout).
• cache from v2 to v3: released in march 2022 (https://github.com/actions/cache).
• upload-artifactfrom 'main' to v3: released in march 2022 (https://github.com/actions/upload-artifact).

This PR also updates Ubuntu runners from 18.04 to 20.04 as per deprecation notice by GitHub which will be unsupported by the 1st of Descember 2022 (see 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/)

[codecov-commenter]

Codecov Report

Merging #594 (f427c97) into v2-branch (3c89c7f) will not change coverage. The diff coverage is n/a.

@@             Coverage Diff             @@
##           v2-branch      #594   +/-   ##
===========================================
  Coverage     100.00%   100.00%           
===========================================
  Files              2         2           
  Lines             10        10           
===========================================
  Hits              10        10           

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[gaborcsardi]

Thanks! I updated these in separate commits, so I think this PR is not needed any more. I am sorry for not merging it, please let me know if something still needs an update.

[mcanouil]

No worries as long as it's done 😉

[github-actions[bot]]

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