Minor Cleanup of spec language

Mostly I wanted to remove the "blacklist" usage, per our styleguide on
culturally sensitive language.

spec/lib/gitlab/import_export/attribute_configuration_spec.rb

@@ -35,8 +35,9 @@ RSpec.describe 'Import/Export attribute configuration' do
     <<-MSG
       It looks like #{relation_class}, which is exported using the project Import/Export, has new attributes: #{new_attributes.join(',')}
 
-      Please add the attribute(s) to SAFE_MODEL_ATTRIBUTES if you consider this can be exported.
-      Please blacklist the attribute(s) in IMPORT_EXPORT_CONFIG by adding it to its correspondent
+      Please add the attribute(s) to SAFE_MODEL_ATTRIBUTES if they can be exported.
+
+      Please denylist the attribute(s) in IMPORT_EXPORT_CONFIG by adding it to its corresponding
       model in the +excluded_attributes+ section.
 
       SAFE_MODEL_ATTRIBUTES: #{File.expand_path(safe_attributes_file)}

spec/lib/gitlab/import_export/references_configuration_spec.rb

@@ -38,8 +38,9 @@ RSpec.describe 'Import/Export Project configuration' do
     <<-MSG
       It looks like #{relation_class}, which is exported using the project Import/Export, has references: #{prohibited_keys.join(',')}
 
-      Please replace it with actual relation in IMPORT_EXPORT_CONFIG if you consider this can be exported.
-      Please blacklist the attribute(s) in IMPORT_EXPORT_CONFIG by adding it to its correspondent
+      Please replace it with actual relation in IMPORT_EXPORT_CONFIG if they can be exported.
+
+      Please denylist the attribute(s) in IMPORT_EXPORT_CONFIG by adding it to its corresponding
       model in the +excluded_attributes+ section.
 
       IMPORT_EXPORT_CONFIG: #{Gitlab::ImportExport.config_file}