Swift: Fix the SQL injection test.

Author: geoffw0

swift/ql/test/query-tests/Security/CWE-089/sqlite3_c_api.swift

@@ -6,8 +6,8 @@ struct URL
 	init?(string: String) {}
 	init?(string: String, relativeTo: URL?) {}
 }
-
-struct Data {
+protocol DataProtocol { }
+struct Data : DataProtocol {
 	init<S>(_ elements: S) { count = 0 }
 
 	var count: Int