Fix the S3 downloading functionality by passing in the AWS region

[ThomasHickman]

If you use the S3 downloading functionality on a local machine, the downloading jobs fail with:

+ aws s3 cp s3://bucket/item __out/
fatal error: Could not connect to the endpoint URL: "https://bucket.s3.nov.amazonaws.com/item"

To fix this, I just passed in MINIWDL__TASK_RUNTIME__ENV='{"AWS_DEFAULT_REGION": "<REGION_OF_THE_BUCKET>"}'. It would be great if miniwdl did this itself at

miniwdl/WDL/runtime/download.py

Lines 316 to 322 in beaa9a9

	try:
	b3creds = boto3.session.Session().get_credentials()
	host_aws_credentials["AWS_ACCESS_KEY_ID"] = b3creds.access_key
	host_aws_credentials["AWS_SECRET_ACCESS_KEY"] = b3creds.secret_key
	host_aws_credentials["AWS_SESSION_TOKEN"] = b3creds.token
	except Exception:
	pass

though.