Require macOS 12 (#59)

And fix deprecation warning.

Author: yim-lee

Package.swift

@@ -5,7 +5,7 @@ import PackageDescription
 let package = Package(
     name: "swift-package-collection-generator",
     // Required for JSONEncoder/Decoder formatting and ISO-8601 support
-    platforms: [.macOS("10.15.4")],
+    platforms: [.macOS(.v12)],
     products: [
         .executable(name: "package-collection-generate", targets: ["PackageCollectionGenerator"]),
         .executable(name: "package-collection-sign", targets: ["PackageCollectionSigner"]),

Sources/Utilities/Logging.swift

@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift Package Collection Generator open source project
 //
-// Copyright (c) 2020 Apple Inc. and the Swift Package Collection Generator project authors
+// Copyright (c) 2020-2023 Apple Inc. and the Swift Package Collection Generator project authors
 // Licensed under Apache License v2.0
 //
 // See LICENSE.txt for license information
@@ -52,7 +52,7 @@ private final class InteractiveWriter {
             term.write(string, inColor: color, bold: bold)
             term.endLine()
         } else {
-            self.stream <<< string
+            self.stream.send(string)
             self.stream.flush()
         }
     }