Fix typo in SftpFileSytemInformation class name

[drieseng]

Notice that we have a typo in the name of this class.

@WojciechNagorski @Rob-Hague: Do we fix this?

[Rob-Hague]

Seems sensible

[drieseng]

@Rob-Hague, this is of course a breaking change. I'm ok with this though.

If we fix this, the SA1649 suppression - which I'll add in my next PR - can be removed from this type.

[Rob-Hague]

Sounds good to me