test(queue_sender): stop the reupload-cleanup tests depending on an ambient region

CI fails these 8 tests with `botocore.exceptions.NoRegionError`. `index.py` builds
its sqs/s3/cloudwatch clients at module scope, and the `mock_env` fixture set every
other environment variable the module needs but not a region — so the tests
silently inherited one from the developer's environment, passed locally, and failed
in CI.

Reproduced under CI conditions locally (region, profile and credential files all
unset): 8 failed before, 8 pass after, and they still pass with a region present.

Not caused by this PR — it blocks it. The test workflow runs on pull requests only,
so a push to develop does not run the suite, which is how it got in.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: rstrahan

src/lambda/queue_sender/test_index.py

@@ -30,6 +30,11 @@ def mock_env():
         "OUTPUT_BUCKET": "test-output-bucket",
         "CONFIG_TABLE": "test-config-table",
         "LOG_LEVEL": "INFO",
+        # index.py builds boto3 clients (sqs/s3/cloudwatch) which need a region.
+        # Without this the tests inherit one from the developer's environment and
+        # pass locally, then fail in CI with NoRegionError — which is exactly what
+        # happened. A unit test must not depend on ambient AWS configuration.
+        "AWS_DEFAULT_REGION": "us-east-1",
     }
     with patch.dict(os.environ, env_vars):
         yield