Guard against missing namespace_settings

In some cases, namespace_settings can be absent; other code accessing
this from group have similar implementations of safe navigation.

Making this change also exposed that Project#adjourned_deletion?,
despite the boolean promise implied by ?, can also return a nil for some
cases. All calls to this method test for boolean, relying on Ruby
interpreting nil as false, so this one test, explicitly testing for
nil-ness, fails.

ee/app/models/ee/project.rb

@@ -930,9 +930,13 @@ module EE
       end
     end
 
-    # Return the group's setting for delayed deletion, false for user namespace projects
+    # Return the group's setting for delayed deletion, false for user namespace
+    #   projects
+    #
     def group_deletion_mode_configured?
-      group && group.namespace_settings.delayed_project_removal?
+      return false unless group&.namespace_settings
+
+      group.namespace_settings.delayed_project_removal?
     end
 
     def latest_ingested_security_pipeline

ee/spec/models/project_spec.rb

@@ -2953,7 +2953,7 @@ RSpec.describe Project do
       end
 
       it 'deletes immediately' do
-        expect(user_project.adjourned_deletion?).to be nil
+        expect(user_project.adjourned_deletion?).to be_falsey
       end
     end
   end