When running sam build --beta-features with a custom runtime targeting ARM64, the build fails with an error about missing architecture support.

Steps to reproduce

1. Create a SAM template with Runtime: provided.al2023 and Architectures: [arm64]
2. Run sam build --beta-features

Expected behavior

Build should succeed and produce an ARM64 binary.

Actual behavior

Build fails with: Error: Architecture arm64 is not supported for runtime provided.al2023

Environment

• SAM CLI version: 1.120.0
• OS: macOS 14.5 (Apple Silicon)
• Docker: 25.0.3