Remove deprecated images from CI and release-script

[AyanSinhaMahapatra]

The following images are deprecated in GitHub actions and Azure DevOps:

• ubuntu-18.04 : https://github.com/actions/runner-images/issues/6002
• macos-10.15 : https://github.com/actions/runner-images/issues/5583

Due to this there was failing tests due to planned brownouts.

Signed-off-by: Ayan Sinha Mahapatra [email protected]

Tasks

• [x] Reviewed contribution guidelines
• [x] PR is descriptively titled 📑 and links the original issue above 🔗
• [x] Tests pass -- look for a green checkbox ✔️ a few minutes after opening your PR Run tests locally to check for errors.
• [x] Commits are in uniquely-named feature branch and has no merge conflicts 📁

[pombredanne]

Thanks! I would like to keep the 10.15 images and deprecated things up to the end if possible :slightly_smiling_face: so we can keep the PR open but not merged just now