Bump built_value_generator in /desktop_photo_search/material (#1096)

Bumps [built_value_generator](https://github.com/google/built_value.dart) from 8.1.4 to 8.2.0.
- [Release notes](https://github.com/google/built_value.dart/releases)
- [Changelog](https://github.com/google/built_value.dart/blob/master/CHANGELOG.md)
- [Commits](https://github.com/google/built_value.dart/compare/v8.1.4...v8.2.0)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

desktop_photo_search/material/pubspec.lock

@@ -105,7 +105,7 @@ packages:
       name: built_value_generator
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "8.1.4"
+    version: "8.2.0"
   characters:
     dependency: transitive
     description: