Test that activities with multiple values for "type" field are supported

[Minoru]

ActivityStreams Vocabulary says that a type can have multiple values; there's also an example of this in ActivityStreams Core spec. However, I found that only a few implementations support this. I think this ability is useful when extending AS Vocabulary, so it'd be nice to have a test for this to push implementations towards conformance.

Note that e.g. Misskey plans to implement this by using the first value of the array. The test should anticipate that, and try different permutations so the AS Vocab type is not always at the 0th position.