accept 'topics' property in pubspec.yaml (#3796)

lib/src/validator/pubspec_typo.dart

diff --git a/lib/src/validator/pubspec_typo.dart b/lib/src/validator/pubspec_typo.dart
index f92a894..c51c678 100644
--- a/lib/src/validator/pubspec_typo.dart
+++ b/lib/src/validator/pubspec_typo.dart
@@ -69,4 +69,5 @@
   'screenshots',
   'platforms',
   'funding',
+  'topics',
 ];