Fix Swift concurrency error in tests

Add @mainactor to SwiftDataTablesTests class to allow creating
SwiftDataTable (a UIView subclass) in test methods.

Author: pavankataria

Example/SwiftDataTablesTests/SwiftDataTablesTests.swift

@@ -10,6 +10,7 @@ import XCTest
 import UIKit
 @testable import SwiftDataTables
 
+@MainActor
 class SwiftDataTablesTests: XCTestCase {
 
     func test_swiftDataTable_withConfigurationOptions_initialises() {