Fix pre-existing HintCode.UNNECESSARY_TYPE_CHECK_TRUE

pkgs/yaml/lib/src/scanner.dart

diff --git a/pkgs/yaml/lib/src/scanner.dart b/pkgs/yaml/lib/src/scanner.dart
index 5cb329a..fdf9277 100644
--- a/pkgs/yaml/lib/src/scanner.dart
+++ b/pkgs/yaml/lib/src/scanner.dart
@@ -309,7 +309,7 @@
     var token = _tokens.removeFirst();
     _tokenAvailable = false;
     _tokensParsed++;
-    _streamEndProduced = token is Token && token.type == TokenType.streamEnd;
+    _streamEndProduced = token.type == TokenType.streamEnd;
     return token;
   }