New preview workflow to work on external forks

[ccarouge]

ACCESS Community Hive

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Description

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Please also include relevant motivation and context.

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Fixes #121

Based on https://securitylab.github.com/research/github-actions-preventing-pwn-requests/, we split the preview workflow in 2 steps: the first builds the site securely and the second deploys the site preview.

Type of change

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• Bug fix (non-breaking change which fixes an issue, e.g. dead links)

Checklist:

• The new content is accessible and located in the appropriate section.
• I have checked my code/text and corrected any misspellings

Please tag the reviewers team in a comment below by prepending an @ in front of ACCESS-Hive/reviewers when ready.

[ccarouge]

It's normal that a preview is not built. The workflow_run steps runs in the context of the main branch and there is no such step yet on that branch. So only the first part of the workflow is run since it's triggered by pull_request which runs within the context of the pull request merge.