Fix "async" config setup

DfE::Analytics initialisation code was ignoring the
"config.async = false" option when provided, and setting it to
"config.async = true" anyways.

This was caused by the conditional assignment operator "||=".

"foo ||= true" does set 'foo' as 'true' if it was either 'nil' or
'false'.

lib/dfe/analytics.rb

@@ -75,7 +75,6 @@ def self.configure
       config.bigquery_timeout                 ||= 120
       config.environment                      ||= ENV.fetch('RAILS_ENV', 'development')
       config.log_only                         ||= false
-      config.async                            ||= true
       config.queue                            ||= :default
       config.user_identifier                  ||= proc { |user| user&.id }
       config.entity_table_checks_enabled      ||= false
@@ -84,6 +83,7 @@ def self.configure
       config.azure_federated_auth             ||= false
       config.excluded_paths                   ||= []
       config.excluded_models_proc             ||= proc { |_model| false }
+      config.async = true if config.async.nil?
 
       return unless config.azure_federated_auth
 

spec/dfe/analytics_spec.rb

@@ -189,6 +189,28 @@
     end
   end
 
+  describe '.async?' do
+    context 'when the async config has been set to true' do
+      before do
+        described_class.configure { |config| config.async = true }
+      end
+
+      it 'returns true' do
+        expect(described_class.async?).to be true
+      end
+    end
+
+    context 'when the async config has been set to false' do
+      before do
+        described_class.configure { |config| config.async = false }
+      end
+
+      it 'returns false' do
+        expect(described_class.async?).to be false
+      end
+    end
+  end
+
   describe '.extract_model_attributes' do
     with_model :Candidate do
       table do |t|