[pigeon] Enable NNBD in tool (#1532)

Opts Pigeon into running in NNBD mode. All of the code had already been converted.

Also updates a legacy Dart command (dart pub run) in the test script to the modern version.
diff --git a/packages/pigeon/CHANGELOG.md b/packages/pigeon/CHANGELOG.md
index 97bd5df..d848818 100644
--- a/packages/pigeon/CHANGELOG.md
+++ b/packages/pigeon/CHANGELOG.md
@@ -1,3 +1,8 @@
+## 3.0.1
+
+* Enables NNBD for the Pigeon tool itself.
+* [tests] Updates legacy Dart commands.
+
 ## 3.0.0
 
 * **BREAKING CHANGE**: Removes the `--dart_null_safety` flag. Generated Dart
diff --git a/packages/pigeon/bin/pigeon.dart b/packages/pigeon/bin/pigeon.dart
index cc6ae02..b96295a 100644
--- a/packages/pigeon/bin/pigeon.dart
+++ b/packages/pigeon/bin/pigeon.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.2
-
 import 'dart:io' show exit;
 
 import 'package:pigeon/pigeon_cl.dart';
diff --git a/packages/pigeon/bin/run_tests.dart b/packages/pigeon/bin/run_tests.dart
index a65d02e..bd4629c 100644
--- a/packages/pigeon/bin/run_tests.dart
+++ b/packages/pigeon/bin/run_tests.dart
@@ -209,7 +209,6 @@
     bool streamOutput = true}) async {
   const bool hasDart = false;
   final List<String> args = <String>[
-    'pub',
     'run',
     'pigeon',
     '--input',
diff --git a/packages/pigeon/lib/generator_tools.dart b/packages/pigeon/lib/generator_tools.dart
index 5b9ac85..65397d9 100644
--- a/packages/pigeon/lib/generator_tools.dart
+++ b/packages/pigeon/lib/generator_tools.dart
@@ -8,7 +8,7 @@
 import 'ast.dart';
 
 /// The current version of pigeon. This must match the version in pubspec.yaml.
-const String pigeonVersion = '3.0.0';
+const String pigeonVersion = '3.0.1';
 
 /// Read all the content from [stdin] to a String.
 String readStdin() {
diff --git a/packages/pigeon/pubspec.yaml b/packages/pigeon/pubspec.yaml
index b7911ae..bd17ad5 100644
--- a/packages/pigeon/pubspec.yaml
+++ b/packages/pigeon/pubspec.yaml
@@ -2,7 +2,7 @@
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/main/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3Apigeon
-version: 3.0.0 # This must match the version in lib/generator_tools.dart
+version: 3.0.1 # This must match the version in lib/generator_tools.dart
 
 environment:
   sdk: ">=2.12.0 <3.0.0"