Fix Sidekiq code reloading

During development, changing backend code causes Sidekiq to reload and
spew, "A copy of Gitlab::SidekiqMiddleware::AdminMode::Client has been
removed from the module tree but is still active!" errors.

To fix this, https://stackoverflow.com/a/29710188 mentions adding `::`
to `Example` helps because this causes `Object.const_missing` instead of
`Example.const_missing`.

lib/gitlab/sidekiq_middleware.rb

@@ -9,18 +9,18 @@ module Gitlab
     # eg: `config.server_middleware(&Gitlab::SidekiqMiddleware.server_configurator)`
     def self.server_configurator(metrics: true, arguments_logger: true, memory_killer: true, request_store: true)
       lambda do |chain|
-        chain.add Gitlab::SidekiqMiddleware::Monitor
-        chain.add Gitlab::SidekiqMiddleware::ServerMetrics if metrics
-        chain.add Gitlab::SidekiqMiddleware::ArgumentsLogger if arguments_logger
-        chain.add Gitlab::SidekiqMiddleware::MemoryKiller if memory_killer
-        chain.add Gitlab::SidekiqMiddleware::RequestStoreMiddleware if request_store
-        chain.add Gitlab::SidekiqMiddleware::BatchLoader
-        chain.add Labkit::Middleware::Sidekiq::Server
-        chain.add Gitlab::SidekiqMiddleware::InstrumentationLogger
-        chain.add Gitlab::SidekiqMiddleware::AdminMode::Server
-        chain.add Gitlab::SidekiqStatus::ServerMiddleware
-        chain.add Gitlab::SidekiqMiddleware::WorkerContext::Server
-        chain.add Gitlab::SidekiqMiddleware::DuplicateJobs::Server
+        chain.add ::Gitlab::SidekiqMiddleware::Monitor
+        chain.add ::Gitlab::SidekiqMiddleware::ServerMetrics if metrics
+        chain.add ::Gitlab::SidekiqMiddleware::ArgumentsLogger if arguments_logger
+        chain.add ::Gitlab::SidekiqMiddleware::MemoryKiller if memory_killer
+        chain.add ::Gitlab::SidekiqMiddleware::RequestStoreMiddleware if request_store
+        chain.add ::Gitlab::SidekiqMiddleware::BatchLoader
+        chain.add ::Labkit::Middleware::Sidekiq::Server
+        chain.add ::Gitlab::SidekiqMiddleware::InstrumentationLogger
+        chain.add ::Gitlab::SidekiqMiddleware::AdminMode::Server
+        chain.add ::Gitlab::SidekiqStatus::ServerMiddleware
+        chain.add ::Gitlab::SidekiqMiddleware::WorkerContext::Server
+        chain.add ::Gitlab::SidekiqMiddleware::DuplicateJobs::Server
       end
     end
 
@@ -29,12 +29,12 @@ module Gitlab
     # eg: `config.client_middleware(&Gitlab::SidekiqMiddleware.client_configurator)`
     def self.client_configurator
       lambda do |chain|
-        chain.add Gitlab::SidekiqStatus::ClientMiddleware
-        chain.add Gitlab::SidekiqMiddleware::ClientMetrics
-        chain.add Gitlab::SidekiqMiddleware::WorkerContext::Client # needs to be before the Labkit middleware
-        chain.add Labkit::Middleware::Sidekiq::Client
-        chain.add Gitlab::SidekiqMiddleware::AdminMode::Client
-        chain.add Gitlab::SidekiqMiddleware::DuplicateJobs::Client
+        chain.add ::Gitlab::SidekiqStatus::ClientMiddleware
+        chain.add ::Gitlab::SidekiqMiddleware::ClientMetrics
+        chain.add ::Gitlab::SidekiqMiddleware::WorkerContext::Client # needs to be before the Labkit middleware
+        chain.add ::Labkit::Middleware::Sidekiq::Client
+        chain.add ::Gitlab::SidekiqMiddleware::AdminMode::Client
+        chain.add ::Gitlab::SidekiqMiddleware::DuplicateJobs::Client
       end
     end
   end