Request for testing of release candidate pyhf v0.7.0rc4

[pyhf announcements]

Dear pyhf users,

We'd like to (belatedly) solicit testing of release candidate pyhf v0.7.0rc4, which is out now on PyPI. v0.7.0rc4 is the fourth and (planned) final release candidate for minor release v0.7.0, and is ready for API testing, and for testing correctness and performance.

To install the release candidate you can either use pip install's --pre flag

```

python -m pip install --upgrade --pre pyhf

```

or specify the version number exactly

```

python -m pip install --upgrade 'pyhf==0.7.0rc4'

```

We welcome any feedback and questions that you have on GitHub Issues and Discussions. As a reminder, v0.7.0 will not contain all requested features made since the last release, and we instead plan to increase the future release cadence with smaller releases to better roll out new features and fixes faster.

Please don't hesitate to contact us through the recommended channels!

Best,
The pyhf dev team (Lukas, Matthew, and Giordon)