fix(ci): create one layer artifact per region & merge

[heitorlessa]

Issue number: #3780

Summary

This PR addresses the new racing condition introduced in upload-artifact@v4.

Previously, we were updating every Layer ARN deployment output to the same artifact name. In V4, an explicit overwrite flag is required, which raises on race conditions (good behavior!).

Now, we upload every layer artifact with the region suffix, then merge all artifacts upon download. Everything else remains the same.

Changes

Please provide a summary of what's being changed

• Write-only instead of append layer artifact txt
• Use region suffix on upload-artifact
• Use pattern instead of name in download-artifact to be able to merge multiple artifacts

User experience

Please share what the user experience looks like before and after this change

Checklist

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• Meet tenets criteria
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented
• PR title follows conventional commit semantics

Is this a breaking change?

RFC issue number:

Checklist:

• Migration process documented
• Implement warnings (if it can live side by side)

Acknowledgment

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[heitorlessa]

We carried out tests on a separate @dreamorosi repo: https://github.com/dreamorosi/actions-playground/blob/c2189e306b4b657b52cc650dec7123cc780cb061/.github/workflows/test.yml#L60

TypeScript related PR: aws-powertools/powertools-lambda-typescript#2095

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues

Measures
0 Security Hotspots
No data about Coverage
2.2% Duplication on New Code

See analysis details on SonarCloud

[dreamorosi]

LGTM, thanks for teaming up.

It's been fun!