feat(tests): add upgrade_step3 mark to Plutus V3 test

Add the @pytest.mark.upgrade_step3 decorator to the
test_plutusv3_builtins method in the Plutus V3 builtins test suite.
This enables selective test execution for upgrade step 3 scenarios.

Author: mkoura

cardano_node_tests/tests/tests_plutus_v3/test_mint_build.py

@@ -186,6 +186,7 @@ def run_scenario(
     @allure.link(helpers.get_vcs_link())
     @pytest.mark.long
     @pytest.mark.team_plutus
+    @pytest.mark.upgrade_step3
     def test_plutusv3_builtins(
         self,
         update_cost_model: None,  # noqa: ARG002