AWS Lambda: Fix capturing errors during AWS Lambda INIT phase (#3943)

The AWS integration fails to capture errors during the INIT phase (at least in Python 3.8 and above environments).

It appears tests for this were disabled after a change in AWS' own runtime environment: #3592

A change from a few months ago where it seems like string serialisation of the JSON payload was disabled and instead the `post_init_error` is invoked directly with the json payload: aws/aws-lambda-python-runtime-interface-client@a37a43a#diff-4513a869520b19ae4e30058106d7c3b5ddbb79216b5e9bd922d83389fb86c603R483

This breaks and causes an error internally when trying to parse the string back into json, and the error is actually swallowed because of `with capture_internal_exceptions()`.

Co-authored-by: Anton Pirker <anton.pirker@sentry.io>

sentry_sdk/integrations/aws_lambda.py

@@ -61,7 +61,10 @@ def sentry_init_error(*args, **kwargs):
 
             else:
                 # Fall back to AWS lambdas JSON representation of the error
-                sentry_event = _event_from_error_json(json.loads(args[1]))
+                error_info = args[1]
+                if isinstance(error_info, str):
+                    error_info = json.loads(error_info)
+                sentry_event = _event_from_error_json(error_info)
                 sentry_sdk.capture_event(sentry_event)
 
         return init_error(*args, **kwargs)

tests/integrations/aws_lambda/test_aws.py

@@ -316,9 +316,6 @@ def test_handler(event, context):
     }
 
 
-@pytest.mark.xfail(
-    reason="Amazon changed something (2024-10-01) and on Python 3.9+ our SDK can not capture events in the init phase of the Lambda function anymore. We need to fix this somehow."
-)
 def test_init_error(run_lambda_function, lambda_runtime):
     envelope_items, _ = run_lambda_function(
         LAMBDA_PRELUDE