Update microbatch tests to handle update wherein incremental strategi…

…es are always validated

dbt-adapters updated the incremental_strategy validation of incremental models such that
the validation now _always_ happens when an incremental model is executed. A test in dbt-core
`TestMicrobatchCustomUserStrategyEnvVarTrueInvalid` was previously set to _expect_ buggy behavior
where an incremental model would succeed on it's "first"/"refresh" run even if it had an invalid
incremental strategy. Thus we needed to update this test in dbt-core to expect the now correct
behavior of incremental model execution time validation

tests/functional/microbatch/test_microbatch.py

@@ -162,11 +162,8 @@ def test_use_custom_microbatch_strategy_env_var_true_invalid_incremental_strateg
         with mock.patch.object(
             type(project.adapter), "valid_incremental_strategies", lambda _: []
         ):
-            # Initial run
-            with patch_microbatch_end_time("2020-01-03 13:57:00"):
-                run_dbt(["run"])
-
-            # Incremental run fails
+            # Run of microbatch model while adapter doesn't have a "valid"
+            # microbatch strategy causes an error to be raised
             with patch_microbatch_end_time("2020-01-03 13:57:00"):
                 _, logs = run_dbt_and_capture(["run"], expect_pass=False)
             assert "'microbatch' is not valid" in logs