Improve and fix integration tests

[nhinsch]

Regenerates the snapshots to reflect the latest changes to the Lambda Extension.

Also, fix some issues with the integration tests:

• Only build the amd64 version of the extension. Right now we don't have any tests that use the arm64 extension so it's a waste of time to build it. In the future, we could add tests for arm64 and parallelize the builds/tests.
• Fix the behavior of boolean arguments. Previously, some boolean arguments like BUILD_EXTENSION=true used the -n operator which checks for a non-empty string. This means that BUILD_EXTENSION=false would be interpreted as true because "false" is a non-empty string. This PR fixes that behavior.
• Stop testing with sandbox Lambda Layers. Previously, we tested the extension with the latest versions of the runtime Lambda layers from the sandbox account. However, because this account is a test environment, there was no guarantee that we were using layers that would behave as expected. This PR updates the tests to use layers from the production account. Because it's harder to get the latest layer version across accounts, the tests default to a hardcoded layer version. If we don't keep this fully up-to-date, it's not the end of the world, because the extension is supposed to work with older versions of the Lambda Layers anyway.

[maxday]

oups sorry about that :)

[maxday]

LGTM!
(I think layer 65 is available for NodeJS if you want to update it right now, otherwise let's merge it!)