[native_assets] Don't auto-roll deps (#151636)

Stop trying to roll the dependencies for native assets automatically.

They are under active development (pre 1.0.0), and have frequent breaking changes. I'll be rolling these manually.
(We have the same setup in the Dart SDK, not auto-rolling dart-lang/native via DEPS.)

Related comment:

* flutter/flutter#151539 (comment)

packages/flutter_tools/lib/src/update_packages_pins.dart

@@ -22,6 +22,8 @@ const Map<String, String> kManuallyPinnedDependencies = <String, String>{
   // Add pinned packages here. Please leave a comment explaining why.
   'flutter_gallery_assets': '1.0.2', // Tests depend on the exact version.
   'flutter_template_images': '4.2.0', // Must always exactly match flutter_tools template.
+  'native_assets_builder': '0.8.0', // Under active development with breaking changes until 1.0.0. Manually rolled by @dcharkes.
+  'native_assets_cli': '0.7.0', // Under active development with breaking changes until 1.0.0. Manually rolled by @dcharkes.
   'material_color_utilities': '0.11.1', // Keep pinned to latest until 1.0.0.
   'leak_tracker': '10.0.5', // https://github.com/flutter/devtools/issues/3951
   'leak_tracker_testing': '3.0.1', // https://github.com/flutter/devtools/issues/3951