fix(aws-lambda): Don't assume the context has client_context

Read client_context and its custom dict with getattr, so a context
object without them falls back to the event headers.

Co-Authored-By: Johannes Daxböck <114897+dingsdax@users.noreply.github.com>

Author: sentry-junior[bot]

sentry_sdk/integrations/aws_lambda/_handler.py

@@ -190,13 +190,10 @@ def sentry_handler(
             # a synchronous `Invoke` passes the invoking span in `ClientContext`; it wins over
             # event headers, which a forwarded HTTP event keeps from further upstream.
             # https://docs.aws.amazon.com/lambda/latest/dg/python-context.html
-            client_context = aws_context.client_context
-            if (
-                client_context is not None
-                and client_context.custom
-                and SENTRY_TRACE_HEADER_NAME in client_context.custom
-            ):
-                sentry_sdk.continue_trace(client_context.custom)
+            client_context = getattr(aws_context, "client_context", None)
+            custom = getattr(client_context, "custom", None)
+            if custom and SENTRY_TRACE_HEADER_NAME in custom:
+                sentry_sdk.continue_trace(custom)
             else:
                 sentry_sdk.continue_trace(headers)
             Scope.set_custom_sampling_context(sampling_context)