mypy test data to pytest-mypy-plugins

migrate-to-pytest-mypy-plugins.py

outputs=[]
with open('graphene_plugin.test', 'r') as f:
    for x in f.read().strip().splitlines():
        if x.startswith("[case "):
            outputs.append(f"- case: {x.replace('[case', '').replace(']', '').strip()}")
            outputs.append("  main: |")
        elif x == "[out]":
            outputs.append("  out: |")
        else:
            outputs.append(f"    {x}")