Non-deterministic selection of Lambda image

[jakob-keller]

At aiobotocore, we use moto as part of our test suite. We recently started to run CI on arm64 runners and noticed frequent failures due to docker related issues, triggered by moto-backed tests performing Lambda invokations. It turned out that the outdated lambci/lambda images are not available for arm64 and thus causing the failures.

Unfortunately, it appears to be impossible to force moto to reliably pick mlupin/docker-lambda due to the way moto determines the Lambda image to use:

moto/moto/awslambda/models.py

Lines 1025 to 1033 in fc7bcea

	# We'll cycle through all of them - when we find the repo that contains our image, we use it
	image_repos = set(
	[
	settings.moto_lambda_image(),
	"mlupin/docker-lambda",
	"lambci/lambda",
	]
	)
	for image_repo in image_repos:

The order in which images are picked in non-deterministic, due to the Python set being used. I would suggest to make this deterministic and will provide a PR shortly.

[jakob-keller]

I can confirm that moto 5.1.0 includes the fix from #8603 and resolves CI flakiness on arm64 for us. Thanks for the quick release!