test(react): align input_context description expectation

Author: vicentereig

spec/unit/dspy/re_act_field_descriptions_spec.rb

@@ -54,7 +54,7 @@ class TestSignature < DSPy::Signature
       input_schema = thought_signature.input_json_schema
       input_context_description = input_schema.dig(:properties, :input_context, :description)
       expect(input_context_description).to be_a(String)
-      expect(input_context_description).to include('Serialized representation')
+      expect(input_context_description).to include('original input fields')
     end
 
     it 'includes description for history field' do
@@ -145,4 +145,4 @@ class TestSignature < DSPy::Signature
       expect(action_property[:enum]).to include('github_list_issues')
     end
   end
-end
+end