fix(server): configure STS region for IRSA

Resolves N/A

Fixes the IRSA ExAws configuration so the global STS client uses the same S3 region source as the S3 client. Without this, ExAws falls back to us-east-1 for the STS web identity credential refresh even when S3 is configured for eu-west-1, which can break in environments that only allow regional STS egress.

The change keeps the existing in-memory awscli profile for web identity credentials and adds a regression assertion that the IRSA config carries Environment.s3_region(secrets).

How to test locally

• mix format --check-formatted lib/tuist/aws/s3_authentication_config.ex test/tuist/aws/s3_authentication_config_test.exs
• MIX_ENV=test mix run --no-start -e 'ExUnit.start(autorun: false); Code.require_file("test/tuist/aws/s3_authentication_config_test.exs"); result = ExUnit.run(); if result.failures > 0, do: System.halt(1)'
• git diff --check -- server/lib/tuist/aws/s3_authentication_config.ex server/test/tuist/aws/s3_authentication_config_test.exs server/mix.lock

Note: mix test test/tuist/aws/s3_authentication_config_test.exs was attempted, but the local test database migration setup failed before this unit test ran with relation "users" does not exist.