Spans are double-counted in redis when quota is defined for span and span_indexed.

[jjbayer]

A quota like

{
    "id": "foo",
    "categories": ["span", "span_indexed"]
}

increments the redis counter by 2 for each span. This has the effect that rate limits start dropping events earlier than they should.

This PR already contains a test to reproduce the behavior: #4258

[jjbayer]

For regular data categories, this behavior is a feature, not a bug (e.g. error abuse quota categories are defined as [DataCategory.DEFAULT, DataCategory.ERROR, DataCategory.SECURITY]. Only if two data categories represent the same thing does this become a problem, but it's hard to catch in current code.

I browsed sentry-side code and it does not seem like we currently define a suspicious quota as described above. For now, log an error in case quotas like this appear: #4476

[jjbayer]

The error introduced above does not appear, and we will get warned if it does.