Fix older compiler version build issues

Author: toastersocks

Package@swift-5.9.swift

@@ -15,7 +15,6 @@ let package = Package(
     dependencies: [
         // Dependencies declare other packages that this package depends on.
         .package(url: "https://github.com/toastersocks/SwiftCheck", .upToNextMajor(from: "0.13.0")),
-        .package(url: "https://github.com/swiftlang/swift-testing", .upToNextMajor(from: "6.0.0")),
     ],
     targets: [
         // Targets are the basic building blocks of a package. A target can define a module or a test suite.
@@ -28,7 +27,6 @@ let package = Package(
             dependencies: [
                 "Flow",
                 "SwiftCheck",
-                    .product(name: "Testing", package: "swift-testing"),
             ]
         ),
     ]

Tests/FlowTests/FlowTests.swift

@@ -1,3 +1,4 @@
+#if swift(>=6.0)
 import Testing
 @testable import Flow
 import Foundation
@@ -30,3 +31,4 @@ final class FlowTests {
         }
     }
 }
+#endif