Bump ffigen from 6.1.2 to 7.1.0

Bumps [ffigen](https://github.com/dart-lang/ffigen) from 6.1.2 to 7.1.0.
- [Release notes](https://github.com/dart-lang/ffigen/releases)
- [Changelog](https://github.com/dart-lang/ffigen/blob/master/CHANGELOG.md)
- [Commits](https://github.com/dart-lang/ffigen/compare/v6.1.2...v7.1.0)

---
updated-dependencies:
- dependency-name: ffigen
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <support@github.com>

pubspec.yaml

@@ -15,7 +15,7 @@ dependencies:
   image: ^3.2.0
 
 dev_dependencies:
-  ffigen: ^6.0.0 # dart run ffigen
+  ffigen: ">=6.0.0 <8.0.0" # dart run ffigen
   flutter_lints: ^2.0.1
   flutter_test:
     sdk: flutter