Migrate DocumentFileTests to Swift Testing

[leogdion]

@testable import BushelCore
import BushelCoreWax
import XCTest
internal final class DocumentFileTests: XCTestCase {
  internal func testDocumentFileFromInvalidFileURLType() {
    let expectedDoc = DocumentFile<TestFileTypeSpecification>.documentFile(
      from: .temporaryDir
    )
    XCTAssertNil(expectedDoc)
  }
  internal func testDocumentFileFromFileURLType() {
    let expectedDoc = DocumentFile<TestFileTypeSpecification>.documentFile(
      from: .temporaryDir.appendingPathComponent("fake.test")
    )
    XCTAssertNotNil(expectedDoc)
  }
}