Update rails requirement from >= 6.0, < 7.3 to >= 6.0, < 8.1

Updates the requirements on [rails](https://github.com/rails/rails) to permit the latest version.
- [Release notes](https://github.com/rails/rails/releases)
- [Commits](rails/rails@v6.0.0...v8.0.0)

---
updated-dependencies:
- dependency-name: rails
  dependency-type: direct:production
...

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

Gemfile

@@ -5,7 +5,7 @@ git_source(:github) { |repo| "https://github.com/#{repo}.git" }
 
 gemspec
 
-gem "rails", ">= 6.0", "< 7.3"
+gem "rails", ">= 6.0", "< 8.1"
 
 gem "sprockets-rails"