Upgrade to hypothesis v6.0

[kclowes]

• Version: 5.14

What was wrong?

Hypothesis v5 introduced a bunch of deprecation warnings around fixture scoping that need to be addressed before we can upgrade to v6.

How can it be fixed?

Fix deprecation warnings. This will probably best be done in a few, smaller PRs The warnings can be seen on any of our core test CI runs.

[pacrob]

Done!