Bump dio from 5.5.0+1 to 5.6.0 in /example

Bumps [dio](https://github.com/cfug/dio) from 5.5.0+1 to 5.6.0.
- [Release notes](https://github.com/cfug/dio/releases)
- [Commits](cfug/dio@dio_v5.5.0...dio_v5.6.0)

---
updated-dependencies:
- dependency-name: dio
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

example/pubspec.yaml

@@ -9,7 +9,7 @@ environment:
 dependencies:
   flutter:
     sdk: flutter
-  dio: 5.5.0+1
+  dio: 5.6.0
   gal:
     path: ../