fix: replace env var with runtime values in run_sh

[tedim52]

Description:

Env vars weren't being replaced with runtime value in run_sh eg.

def run(plan, args):
    database = plan.add_service(name="database", config=ServiceConfig(image="postgres:latest"))

    plan.run_sh(
        run="echo $VAR_1",
        env_vars={
            "VAR_1": database.ip_address
        }
    )

used to output

Command returned with exit code '0' and the following output:
--------------------
{{kurtosis:b49259098950411ba1e409e8a749c562:ip_address.runtime_value}}
--------------------

but now we get:

 Command returned with exit code '0' and the following output:
--------------------
172.16.24.5
--------------------

Is this change user facing?

YES