Bump dartdoc to 0.28.3+2 (#31148)
Bump dartdoc to 0.28.3+2 (#31148)

This version of dartdoc properly escapes fenced code block "info strings."
flutter/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter