Fix unknown constant in compliance dashboard seed

The following error was encountered when seeding ee/db/fixtures/development/32_compliance_dashboard_merge_requests.rb:

NameError: uninitialized constant Gitlab::Seeder::ComplianceDashboardMergeRequests::AccessDeniedError
(eval):69:in `rescue in create_merge_request!'
(eval):52:in `create_merge_request!'
(eval):48:in `block in merge_requests’
(eval):40:in `map’
(eval):40:in `merge_requests’
(eval):19:in `seed!'
(eval):113:in `block (4 levels) in run_file’
(eval):111:in `each’
(eval):111:in `block (3 levels) in run_file’
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/gitlab/seeder.rb:91:in `block in quiet’
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/gitlab/seeder.rb:122:in `without_statement_timeout’
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/gitlab/seeder.rb:90:in `quiet’
(eval):104:in `block (2 levels) in run_file’
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/tasks/gitlab/setup.rake:36:in `setup_db’
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/tasks/gitlab/setup.rake:7:in `block (2 levels) in <main>'
/Users/ameliabauerly/GitLab/gdk/gitlab/lib/tasks/dev.rake:9:in `block (2 levels) in <main>'
/Users/ameliabauerly/.asdf/installs/ruby/2.7.2/bin/bundle:23:in `load’
/Users/ameliabauerly/.asdf/installs/ruby/2.7.2/bin/bundle:23:in `<main>