[FIX] sale_order_product_recommendation: freezegun hack

As seen in spulec/freezegun#485, when decorating a class with `@freezegun.freeze_time()`, class cleanups are not properly executed.

For Odoo, this means that the cursor is not properly closed. Thus, if you happen to run a test for another module after this one that needs a Postgres-level lock that conflicts with this module's, it will fail.

This change does the same, but without decorating the class. Then, the cleanups work as expected.

@moduon MT-1075

sale_order_product_recommendation/tests/test_recommendation.py

@@ -10,7 +10,6 @@
 from .test_recommendation_common import RecommendationCase
 
 
-@freeze_time("2021-10-02 15:30:00")
 class RecommendationCaseTests(RecommendationCase):
     def test_recommendations(self):
         """Recommendations are OK."""

sale_order_product_recommendation/tests/test_recommendation_common.py

@@ -5,11 +5,14 @@
 from odoo.tests.common import TransactionCase
 
 
-@freeze_time("2021-10-02 15:30:00")
 class RecommendationCase(TransactionCase):
     @classmethod
     def setUpClass(cls):
         super().setUpClass()
+        # HACK https://github.com/spulec/freezegun/issues/485
+        freezer = freeze_time("2021-10-02 15:30:00")
+        freezer.__enter__()
+        cls.addClassCleanup(freezer.__exit__)
         # Remove this variable in v16 and put instead:
         # from odoo.addons.base.tests.common import DISABLED_MAIL_CONTEXT
         DISABLED_MAIL_CONTEXT = {