Fix: add backwards compatibility for clients without public config

lib/active_graphql/client/actions/action/format_inputs.rb

@@ -24,7 +24,7 @@ def call
           attr_reader :inputs, :client
 
           def treat_symbol_as_keyword?
-            client.config[:treat_symbol_as_keyword]
+            client.respond_to?(:config) && client.config[:treat_symbol_as_keyword]
           end
 
           def formatted(attributes, parent_keys: [])

spec/lib/active_graphql/client/actions/action/format_inputs_spec.rb

@@ -32,6 +32,28 @@
           expect(call).to eq 'val: yes'
         end
       end
+
+      context 'when client does not respond to config' do
+        let(:client) { nil }
+
+        it 'converts Symbol values to strings' do
+          expect(call).to eq 'val: "yes"'
+        end
+      end
+
+      context 'when client has config as private method' do
+        let(:client_class) do
+          Class.new(ActiveGraphql::Client::Adapters::GraphlientAdapter) do
+            private :config
+          end
+        end
+
+        let(:client) { client_class.new(client_config) }
+
+        it 'converts Symbol values to strings' do
+          expect(call).to eq 'val: "yes"'
+        end
+      end
     end
 
     context 'when value is nested hash' do