Update CI

[joergbrech]

macos-10.15 will not be available from August 30th 2022.

EDIT:

We critically need to update our CI, as quite a few actions and runners have become deprecated:

• Node.js 12 actions are deprecated. For more information see: https://github.blog/changelog/2022-09-22-github-actions-all-actions-will-begin-running-on-node16-instead-of-node12/. Please update the following actions to use Node.js 16: actions/checkout, nick-invision/retry, hendrikmuhs/ccache-action, actions/upload-artifact, hendrikmuhs/ccache-action, actions/checkout
• The set-output command is deprecated and will be disabled soon. Please upgrade to using Environment Files. For more information see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/
• macos-10.15 will not be available from August 30th 2022. We should use macos-11 or macos-latest
• "The ubuntu-18.04 environment is deprecated, consider switching to ubuntu-20.04(ubuntu-latest), or ubuntu-22.04 instead.": We should test on Ubuntu 20.04 and 22.04.

[joergbrech]

"The ubuntu-18.04 environment is deprecated, consider switching to ubuntu-20.04(ubuntu-latest), or ubuntu-22.04 instead."

[joergbrech]

This has become a high priority issue, because there are several deprecations threatening to break our CI

[AntonReiswich]

Ok, I get onto it.