[Hermetic Build] Changes to helper scripts (e.g. update_generation_config.sh) cannot be automatically updated #3871

Take for example #3853

It brough changes to the config update scripts.

However, downstream libraries would not be able to pull the latest templates because the very source of the new version was fixed in a later template version, leaving the downstream libraries stuck on GENERATOR_VERSION=2.59.0 (which comes from the old endpoint of update_generation_config.sh).

This is a rather unlucky loop because other templates can be normally updated upon each release of sdk-platform-java.

cc: @blakeli0 @zhumin8 @lqiu96