Shutdown engines in test

Add a missing `.shutdown()` in a test engine factory.  The comment was correct
that the _executor_ was not started, but either missed that the status
reporting thread was started, or the rug was changed underneath it.

compute_endpoint/tests/unit/test_gce_container.py

@@ -15,6 +15,8 @@
 
 @pytest.fixture
 def gce_factory(tmp_path, randomstring) -> t.Callable:
+    engines: list[GlobusComputeEngine] = []
+
     def _kernel(**k):
         expect_uri = randomstring(length=random.randint(1, 20))
         expect_opts = randomstring(length=random.randint(1, 20))
@@ -27,16 +29,21 @@ def _kernel(**k):
             **k,
         }
         with mock.patch(f"{_MOCK_BASE}ReportingThread"):
-            gce = GlobusComputeEngine(**k)
-        with mock.patch.object(gce.executor, "start"):
-            gce.start(endpoint_id=uuid.uuid4(), run_dir=tmp_path)
-            assert gce.executor.start.called
+            with mock.patch(f"{_MOCK_BASE}JobStatusPoller"):
+                gce = GlobusComputeEngine(**k)
+                gce.executor.start = mock.Mock()
+                gce.start(endpoint_id=uuid.uuid4(), run_dir=str(tmp_path))
+                assert gce.executor.start.called
+
+                engines.append(gce)
 
-        # No cleanup necessary because executor not started
         return gce, expect_uri, expect_opts
 
     yield _kernel
 
+    for e in engines:
+        e.shutdown()
+
 
 def test_docker(tmp_path, gce_factory):
     gce, exp_uri, exp_opts = gce_factory(container_type="docker")