Account for new generated rules.json location in linter tool (#1956)

In preparation for the linter moving to the SDK, the `rules.json` file
is no longer generated to its own location. The site-www version is
better guaranteed to be up to date and match the `stable` release of
Dart.

experimental/linting_tool/lib/repository/api_provider.dart

@@ -8,15 +8,14 @@ import 'package:linting_tool/model/rule.dart';
 import 'package:yaml/yaml.dart';
 
 class APIProvider {
-  static const String _baseURL = 'https://dart-lang.github.io/linter';
-
   final http.Client httpClient;
 
   APIProvider(this.httpClient);
 
   Future<List<Rule>> getRulesList() async {
-    final response =
-        await httpClient.get(Uri.parse('$_baseURL/lints/machine/rules.json'));
+    final response = await httpClient.get(Uri.parse(
+      'https://raw.githubusercontent.com/dart-lang/site-www/main/src/_data/linter_rules.json',
+    ));
 
     if (response.statusCode == 200) {
       final data = json.decode(response.body) as List;