Make default xfail strict
Pytest let's you configure the default xfail strictness in the `setup.cfg`

```
xfail_strict=true
```

This issue is to

1. Make that change
2. Update tests that are currently XPASSing
    - If always passing then remove the xfail entirely
    - If only sometimes passing (flaky test, dependency, configuration, etc.) then mark that specific test as `strict=False`.

cc @jbrockmendel @jreback 