ci: fix broken dd-trace-py wheel downloading

[brettlangdon]

What does this PR do?

Update the build layer workflow to download ddtrace wheels from the publish S3 bucket: https://dd-trace-py-builds.s3.amazonaws.com/main/index.html instead of from GHA since we have moved wheel building from GHA to GitLab.

Motivation

Testing Guidelines

Additional Notes

Types of Changes

• Bug fix
• New feature
• Breaking change
• Misc (docs, refactoring, dependency upgrade, etc.)

Check all that apply

• This PR's description is comprehensive
• This PR contains breaking changes that are documented in the description
• This PR introduces new APIs or parameters that are documented and unlikely to change in the foreseeable future
• This PR impacts documentation, and it has been updated (or a ticket has been logged)
• This PR's changes are covered by the automated tests
• This PR collects user input/sensitive content into Datadog
• This PR passes the integration tests (ask a Datadog member to run the tests)

[brettlangdon]

/merge

[dd-devflow-routing-codex]

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2026-01-07 15:11:20 UTC ℹ️ Start processing command /merge

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2026-01-07 15:20:46 UTC ℹ️ MergeQueue: merge request added to the queue

The expected merge time in main is approximately 0s (p90).

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2026-01-07 15:54:13 UTC ℹ️ MergeQueue: Retrying because an high priority merge request needed to be processed first. No action is needed from your side.

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2026-01-07 15:54:17 UTC ⚠️ MergeQueue: This merge request build was cancelled

rithika.narayan@datadoghq.com cancelled this merge request build

[rithikanarayan]

/remove

[dd-devflow-routing-codex]

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2026-01-07 15:54:00 UTC ℹ️ Start processing command /remove

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2026-01-07 15:54:12 UTC ℹ️ Devflow: /remove