ref(awslambda): xfail broken tests for now

[sentrivana]

We rely on the log output of our AWS Lambda tests to determine whether the tests have been successful: we log envelope and event contents and then check whether the log output looks as expected.

AWS Lambda has recently started logging a new warning when a function throws an unhandled exception. This is a scenario we're testing in some of our test cases.

The problem is that the log output is limited to the last 4kB and the new warning takes up a lot of space, so some of our events/envelopes will not fit anymore.

xfailing the tests here so that our release is not blocked now, but we'll need a proper solution, see #2795

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[antonpirker]

As a follow on fixing this issue for real we have created this GH Issue: #2795