remove pep257 test for galactic

CMakeLists.txt

@@ -128,15 +128,20 @@ if(BUILD_TESTING)
   find_package(ament_cmake_flake8 REQUIRED)
   find_package(ament_cmake_lint_cmake REQUIRED)
   find_package(ament_cmake_clang_format REQUIRED)
-  find_package(ament_cmake_pep257 REQUIRED)
   find_package(ament_cmake_xmllint REQUIRED)
 
+  if(NOT $ENV{ROS_DISTRO} STREQUAL "galactic")
+    find_package(ament_cmake_pep257 REQUIRED)
+  endif()
+
   ament_copyright()
   ament_cppcheck(LANGUAGE c++)
   ament_cpplint(FILTERS "-build/include,-runtime/indentation_namespace")
   ament_flake8()
   ament_lint_cmake()
-  ament_pep257()
+  if(NOT $ENV{ROS_DISTRO} STREQUAL "galactic")
+    ament_pep257()
+  endif()
   ament_clang_format(CONFIG_FILE .clang-format)
   ament_xmllint()
 endif()