Bump google_fonts from 5.1.0 to 6.0.0 in /experimental/varfont_shader_puzzle (#2017)

Bumps [google_fonts](https://github.com/material-foundation/flutter-packages/tree/main/packages) from 5.1.0 to 6.0.0.
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experimental/varfont_shader_puzzle/pubspec.yaml

@@ -9,7 +9,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  google_fonts: ^5.0.0
+  google_fonts: ^6.0.0
 
 dev_dependencies:
   analysis_defaults: