chore(deps): Bump the built_value group

Bumps the built_value group in /packages/aws_common with 2 updates: [built_value](https://github.com/google/built_value.dart) and [built_value_generator](https://github.com/google/built_value.dart).


Updates `built_value` from 8.7.0 to 8.8.0
- [Release notes](https://github.com/google/built_value.dart/releases)
- [Changelog](https://github.com/google/built_value.dart/blob/master/CHANGELOG.md)
- [Commits](google/built_value.dart@v8.7.0...v8.8.0)

Updates `built_value_generator` from 8.7.0 to 8.8.0
- [Release notes](https://github.com/google/built_value.dart/releases)
- [Changelog](https://github.com/google/built_value.dart/blob/master/CHANGELOG.md)
- [Commits](google/built_value.dart@v8.7.0...v8.8.0)

---
updated-dependencies:
- dependency-name: built_value
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: built_value
- dependency-name: built_value_generator
  dependency-type: direct:production
  update-type: version-update:semver-minor
  dependency-group: built_value
...

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

packages/aws_common/pubspec.yaml

@@ -11,7 +11,7 @@ environment:
 dependencies:
   async: ^2.10.0
   built_collection: ^5.0.0
-  built_value: ">=8.6.0 <8.8.0"
+  built_value: ^8.6.0
   collection: ^1.15.0
   http2: ^2.0.0
   js: ^0.6.4
@@ -29,7 +29,7 @@ dev_dependencies:
   build_runner: ^2.4.0
   build_test: ^2.1.5
   build_web_compilers: ^4.0.0
-  built_value_generator: 8.7.0
+  built_value_generator: 8.8.0
   json_serializable: 6.7.1
   stream_channel: ^2.1.0
   test: ^1.22.1