Tests: Add cryptography back as a dependency for Python integration tests

[reedham-aws]

When modifying integration tests recently, I noticed that the cryptography library had been removed as a dependency for our test applications in our integration tests (explanation here: #8549 (comment)). This was originally because of aws/aws-lambda-builders#29:

aws-sam-cli/tests/integration/testdata/buildcmd/Python/requirements.txt

Lines 7 to 9 in 75bc6c4

	# `cryptography` has a dependency on `pycparser` which, for some reason doesn't build inside a Docker container.
	# Turning this off until we resolve this issue: https://github.com/awslabs/aws-lambda-builders/issues/29
	# cryptography~=2.4

However, that issue has been resolved now. It's probably safe to add cryptography back now, including to files that have been added since, such as https://github.com/aws/aws-sam-cli/blob/develop/tests/integration/testdata/buildcmd/PythonPyProject/pyproject.toml.