[CI] Replace `runs-on: ubuntu-latest` with `runs-on: ubuntu-20.04` in GitHub Action workflows

[lhotari]

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Motivation

The workflows currently contained mixed usage of runs-on: ubuntu-latest and runs-on: ubuntu-20.04. It's better to be consistent and use runs-on: ubuntu-20.04 for all cases. It's better to be able to control when we switch to use ubuntu-22.04 image instead of letting GitHub decide. For macOS, we should replace macos-latest with macos-11 for the similar reason.

Available image definitions are listed at https://github.com/actions/runner-images#available-images

Solution

No response

Alternatives

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Anything else?

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Are you willing to submit a PR?

• [ ] I'm willing to submit a PR!

[tisonkun]

Sounds good! I just do the same thing in incubator-kvrocks days before.