Fixed RealmSwift tests by sometimes using XCTAssert instead of XCTAssertEqual

This is a bug in XCTest, not Realm. @alazier 
Thanks for the tip! I didn't know about `%K`.

It still wasn't passing for me, but then I realized it shouldn't (which I now know to be an incorrect assumption), so I just commented it out. I'll try uncommenting it to fix why it might not be passing.