update artifacts GitHub actions to v4

[alexrashed]

Motivation

GitHub is currently phasing out support for actions/upload-artifact and actions/download-artifact versions other than the latest major release v4: https://github.blog/changelog/2024-04-16-deprecation-notice-v3-of-the-artifact-actions/

Starting December 5, 2024, GitHub Actions customers will no longer be able to use v3 of actions/upload-artifact or actions/download-artifact.

This PR updates the the action to v4.

Changes

Update the GitHub artifact action versions to v4 before the burn-down.

[github-actions]

The ephemeral instance for the application preview has been shut down

[lukqw]

Thanks for pro-actively updating our actions 💪
I've added comments that mainly highlight potentially breaking functionality around ephemeral instances

[alexrashed]

Thanks a lot for your comments, @lukqw!
To be honest, I was a bit confused by the flow of the artifacts when using the action.
The only problem which caused me changing the IDs is that it's not allowed anymore with upload-artifacts@v4 to upload two artifacts with the same ID in the same workflow anymore.
Would you mind taking this PR over and just changing it the way you would know it should be?

[lukqw]

Thanks a lot for your comments, @lukqw!
To be honest, I was a bit confused by the flow of the artifacts when using the action.
The only problem which caused me changing the IDs is that it's not allowed anymore with upload-artifacts@v4 to upload two artifacts with the same ID in the same workflow anymore.
Would you mind taking this PR over and just changing it the way you would know it should be?

@alexrashed
Understandable that the current flow is confusing, it always takes me some time to understand the multi-artifact setup and flow of artifacts as well.
I didn't know that duplicate IDs are no longer allowed and have updated the PR with that in mind.
I've added new logic which downloads the instance-preview-url artifact, which now makes it available to the workflow further down the line, and have verified it to be working.
I've further added a new assertion step to the ephemeral test suite, which verifies whether a preview comment has been added to the PR - this is the functionality that would have been broken.

[alexrashed]

Awesome! Thanks so much for taking over, fixing the issues, and improving the workflow and assertions!
From my perspective the code also looks great! 💯