Ensure correct node/python versions are used

[sidvishnoi]

Users shouldn't need to add a setup-node (for respec) or setup-python (for bikeshed) step. spec-prod should ensure that versions are available, regardless of runs-on value.
GitHub Actions now support using other actions in composite actions (https://github.blog/changelog/2021-08-25-github-actions-reduce-duplication-with-action-composition/) so it should be much simpler now.

Also recommend runs-on: ubuntu-latest instead of ubuntu-20.04 once this issue is closed, so the users don't have to update runs-on when GitHub deprecates old versions.

[martinthomson]

Note that the example workflow (in README.md) doesn't include setup-node steps. We've been following that in some specs and the update to node 16 has caused those builds to fail.

[sidvishnoi]

I will update docs to recommend not using node 16 manually and let it be controlled by spec-prod. Can you share some examples where (and possibly why) manual setup-node was used?

Can't revert it now as all ReSpec based specs will fail otherwise. In near future, it might be possible to detect node version and not run setup-node if an ok version already exists. (actions/runner#834, waiting for actions/runner#1438 to be generally available). Will also enable setup-python for Bikeshed then.

[sidvishnoi]

To be clear, spec-prod doesn't require users to manually use setup-node in their workflows (now it in fact discourages it).
If I understand correctly, you mean it started crashing if there was a manual setup-node in workflow?

[martinthomson]

The last build of https://github.com/w3c/mediacapture-fromelement contains a failure.

[sidvishnoi]

That workflow is using unsupported spec-prod@v1. Please upgrade to v2.
Example upgrade: w3c/webrtc-svc@9412d07

[martinthomson]

Ah, thanks for the correction. I've opened a pull request to fix it.