test(backend): update expected error message for invalid company code to match korean translation

backend/internal/handler/auth_handler_signup_test.go

@@ -119,7 +119,7 @@ func TestSignup_CompanyCodeValidation(t *testing.T) {
 		assert.Equal(t, http.StatusBadRequest, resp.StatusCode)
 		var res map[string]interface{}
 		json.NewDecoder(resp.Body).Decode(&res)
-		assert.Equal(t, "Invalid company code.", res["error"])
+		assert.Equal(t, "해당하는 가족사(테넌트)를 찾을 수 없습니다.", res["error"])
 	})
 
 	t.Run("Active Company Code", func(t *testing.T) {