Interval test skips causing other's to be skipped?
Just saw this, haven't looked yet

test     | pass | skip | xfail
-------- | ---- | ---- | -----
Interval | 551  | 640  | 0
Period   | 472  | 0    | 1
Both     | 789  | 829  | 1

commands:

- `pytest pandas/tests/indexes/period/`
- `pytest pandas/tests/indexes/period/`
- `pytest pandas/tests/indexes/interval/ pandas/tests/indexes/period/`
