GIT_SHALLOW_CLONE is not dynamic applicable after configuration

[adong]

What happened: From https://docs.screwdriver.cd/user-guide/environment-variables, environment variables such as

GIT_SHALLOW_CLONE
GIT_SHALLOW_CLONE_DEPTH
GIT_SHALLOW_CLONE_SINCE	
GIT_SHALLOW_CLONE_SINGLE_BRANCH

are used in setup steps to git clone.

When I define a step that sets the value to deal with this issue but the GIT_SHALLOW_CLONE variable is used before any of the steps in my screwdriver.yaml are run so it's not possible to set it with code in a step.

What you expected to happen: Since the env variable of GIT_SHALLOW_CLONE is used to get the code, changing the environment in the step execution (runtime) is a moot point.

There should be a way to change it in the runtime environment

How to reproduce it: n/a