Fix test failures in aws-sam-translator 1.92.0 by

mocking boto3.Session region

- Added @patch("boto3.Session") to tests in test_serverless_app_plugin.py and
test_region_configuration.py to mock region_name as 'us-east-1', which resolved
NoRegionFound errors.

- Fixed AttributeError in test_sleep_between_sar_checks by correcting variable reference.

- All 4083 tests pass with 95.79% coverage.

fixes #3677

Author: Victorthedev