Maintenance: remove Python 3.9 from layer automation

[dreamorosi]

Why is this needed?

Powertools for AWS Lambda (Python) dropped Python 3.9 support in PR #7807 and release v3.24.0. Commercial Python 3.9 layers intentionally stop at layer version 27.

Partition automation still includes Python 3.9 in deployment, verification, and region bootstrap matrices. Any attempt to process commercial version 28 or later fails with ResourceNotFoundException before supported runtimes can proceed. This happened while aligning China production after version 27.

The stale entries also make the workflows advertise and operate on a runtime that the project no longer builds, tests, documents, or publishes.

Which area does this relate to?

Automation

Solution

Remove Python 3.9 layer entries from active layer automation, including:

• Layer Deployment (Partitions);
• Layer Verification (Partition);
• GovCloud deployment and verification workflows;
• Region Bootstrap;
• any related maintainer documentation or matrices that still expect python39.

Keep existing Python 3.9 version-27 layers available for current users; this change should only stop automation from expecting newer versions.

Acknowledgment

• This request meets Powertools for AWS Lambda (Python) Tenets
• This should be considered in other Powertools for AWS Lambda languages

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