Bump `flutter_markdown` version to latest (#2339)

fixes: https://github.com/flutter/samples/issues/2332

## Pre-launch Checklist

- [x] I read the [Flutter Style Guide] _recently_, and have followed its
advice.
- [x] I signed the [CLA].
- [x] I read the [Contributors Guide].
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] All existing and new tests are passing.

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ai_recipe_generation/pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
   flutter:
     sdk: flutter
   flutter_floating_bottom_bar: ^1.2.0
-  flutter_markdown: ^0.6.20
+  flutter_markdown: ^0.7.3
   flutter_svg: ^2.0.9
   google_fonts: 6.1.0
   google_generative_ai: ^0.4.0

dynamic_theme/pubspec.yaml

@@ -8,7 +8,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  flutter_markdown: ^0.7.1
+  flutter_markdown: ^0.7.3
   google_generative_ai: ^0.4.0
   url_launcher: ^6.2.6
 

experimental/linting_tool/pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
   cupertino_icons: ^1.0.2
   equatable: ^2.0.3
   file_selector: ^1.0.0
-  flutter_markdown: ^0.7.0
+  flutter_markdown: ^0.7.3
   google_fonts: ^6.0.0
   hive: ^2.0.4
   hive_flutter: ^1.1.0

gemini_tasks/pubspec.yaml

@@ -8,7 +8,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  flutter_markdown: ^0.7.1
+  flutter_markdown: ^0.7.3
   google_generative_ai: ^0.4.0
   url_launcher: ^6.2.6