[WIP] AIPMDM-888: Simplify OSS Metaflow core tests to be more Pythonic / pytest-friendly / tox-friendly #2268

Job	Run time
metaflow.s3.minio / Python 3.9 on ubuntu-22.04	8m 16s
metaflow.s3.minio / Python 3.10 on ubuntu-22.04	8m 19s
metaflow.s3.minio / Python 3.8 on ubuntu-22.04	8m 1s
metaflow.s3.minio / Python 3.11 on ubuntu-22.04	8m 17s
metaflow.s3.minio / Python 3.12 on ubuntu-22.04	8m 1s
metaflow.s3.minio / Python 3.8 on ubuntu-22.04	8m 25s
metaflow.s3.minio / Python 3.11 on ubuntu-22.04	8m 25s
metaflow.s3.minio / Python 3.10 on ubuntu-22.04	8m 26s
metaflow.s3.minio / Python 3.12 on ubuntu-22.04	8m 24s
metaflow.s3.minio / Python 3.9 on ubuntu-22.04	8m 8s
metaflow.s3.minio / Python 3.11 on ubuntu-22.04	8m 19s
metaflow.s3.minio / Python 3.10 on ubuntu-22.04	8m 2s
metaflow.s3.minio / Python 3.12 on ubuntu-22.04	8m 20s
metaflow.s3.minio / Python 3.8 on ubuntu-22.04	8m 19s
metaflow.s3.minio / Python 3.9 on ubuntu-22.04	8m 19s
	2h 4m 1s

Provide feedback