fix(test/cleanup): mock _fleet_has_no_remaining_instances on partial-return tests

EC2Fleet partial path now calls _fleet_has_no_remaining_instances, which
runs _collect_with_next_token in a NextToken loop against a MagicMock
ec2_client.  MagicMock.get(...) returns a truthy MagicMock for the
NextToken key, so the loop never terminates — the test hung indefinitely.

SpotFleet partial path has the same defensive call.  Its retry-based
variant returns a MagicMock whose .get('ActiveInstances', []) yields an
empty iterator, which falsely flags the fleet as empty and triggers an
unintended launch-template cleanup, failing the assertion.

Patch _fleet_has_no_remaining_instances to return False on both
partial-return tests so the production code skips the new defensive
check and the original partial-return semantic is exercised.

Author: fgogolli

tests/providers/aws/unit/infrastructure/handlers/test_cleanup.py

@@ -310,6 +310,11 @@ def test_partial_return_does_not_trigger_lt_cleanup(self):
         with (
             patch.object(handler._fleet_release_manager, "_delete_fleet") as mock_delete_fleet,
             patch.object(handler, "_delete_orb_launch_template") as mock_delete_lt,
+            patch.object(
+                handler._fleet_release_manager,
+                "_fleet_has_no_remaining_instances",
+                return_value=False,
+            ),
         ):
             handler._release_hosts_for_single_ec2_fleet(
                 "fleet-123",
@@ -390,7 +395,14 @@ def test_partial_return_does_not_trigger_lt_cleanup(self):
         config_port = _make_config_port()
         handler = _make_spot_fleet_handler(config_port=config_port)
 
-        with patch.object(handler, "_delete_orb_launch_template") as mock_delete_lt:
+        with (
+            patch.object(handler, "_delete_orb_launch_template") as mock_delete_lt,
+            patch.object(
+                handler._release_manager,
+                "_fleet_has_no_remaining_instances",
+                return_value=False,
+            ),
+        ):
             handler._release_hosts_for_single_spot_fleet(
                 "sfr-123",
                 ["i-1"],