Remove warning noise in ProjectImportOptions

Squlches these warnings:

```
/opt/gitlab/embedded/service/gitlab-rails/app/workers/concerns/project_import_options.rb:5: warning: already initialized constant ProjectImportOptions::IMPORT_RETRY_COUNT
/opt/gitlab/embedded/service/gitlab-rails/app/workers/concerns/project_import_options.rb:5: warning: previous definition of IMPORT_RETRY_COUNT was here
```

app/workers/concerns/project_import_options.rb

 module ProjectImportOptions
   extend ActiveSupport::Concern
 
-  included do
-    IMPORT_RETRY_COUNT = 5
+  IMPORT_RETRY_COUNT = 5
 
+  included do
     sidekiq_options retry: IMPORT_RETRY_COUNT, status_expiration: StuckImportJobsWorker::IMPORT_JOBS_EXPIRATION
 
     # We only want to mark the project as failed once we exhausted all retries