Ensure pre_experiment validation has access to plugin configuration

This is a fixup of a regression in 1ae12f6

The bug slipped through as the feature is skipped unless the test is
run on-premise

src/ert/config/ert_config.py

@@ -804,6 +804,7 @@ def _create_list_of_forward_model_steps_to_run(
                         forward_model_steps=[fm_step],
                         skip_pre_experiment_validation=True,
                         env_vars=env_vars,
+                        env_pr_fm_step=cls.ENV_PR_FM_STEP
                     )
                     fm_json_for_validation = dict(substituted_json["jobList"][0])
                     fm_json_for_validation["environment"] = {