Fix bundle issues in test/development

Remove loading a fork when testing against newer
versions of Solidus/Rails.

Now that svenfuchs/routing-filter#76
has been release that's not needed anymore.

We still have to rely on the GitHub version of the gem when
used with Rails 6.1 because the compatibility fix has been
merged but not yet released. see
svenfuchs/routing-filter#75.

Gemfile

@@ -14,10 +14,7 @@ gem 'rails', '>0.a'
 # Provides basic authentication functionality for testing parts of your engine
 # gem 'solidus_auth_devise'
 
-unless %w[v2.9 v2.10].include? branch
-  # We use routing-filter to test the gem only. This version works with Rails 6.1 as well.
-  gem 'routing-filter', github: "hasghari/routing-filter", branch: "rails-6.1" 
-end
+gem 'routing-filter', github: "svenfuchs/routing-filter", branch: "master" 
 
 case ENV['DB']
 when 'mysql'