Upgrade: Bump flipper from 0.28.0 to 0.28.3

Bumps [flipper](https://github.com/jnunemaker/flipper) from 0.28.0 to 0.28.3.
- [Changelog](https://github.com/jnunemaker/flipper/blob/main/Changelog.md)
- [Commits](flippercloud/flipper@v0.28.0...v0.28.3)

---
updated-dependencies:
- dependency-name: flipper
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Gemfile.lock

@@ -187,7 +187,7 @@ GEM
     ffi-compiler (1.0.1)
       ffi (>= 1.0.0)
       rake
-    flipper (0.28.0)
+    flipper (0.28.3)
       concurrent-ruby (< 2)
     flipper-active_record (0.28.0)
       activerecord (>= 4.2, < 8)