tests: Fix deprecation warning for utcfromtimestamp()

Fix DeprecationWarning for datetime.datetime.utcfromtimestamp()

It suggests to use timezone-aware objects to represent datetimes in UTC
with datetime.UTC but datetime.timezone.utc is backwards compatible.

Signed-off-by: Ricardo Branco <rbranco@suse.de>

Author: ricardobranco777

tests/unit/api_container_test.py

@@ -1302,7 +1302,7 @@ def test_log_since_with_float(self):
 
     def test_log_since_with_datetime(self):
         ts = 809222400
-        time = datetime.datetime.utcfromtimestamp(ts)
+        time = datetime.datetime.fromtimestamp(ts, datetime.timezone.utc)
         with mock.patch('docker.api.client.APIClient.inspect_container',
                         fake_inspect_container):
             self.client.logs(fake_api.FAKE_CONTAINER_ID, stream=False,

tests/unit/api_test.py

@@ -232,6 +232,7 @@ def test_events(self):
     def test_events_with_since_until(self):
         ts = 1356048000
         now = datetime.datetime.utcfromtimestamp(ts)
+        now = datetime.datetime.fromtimestamp(ts, datetime.timezone.utc)
         since = now - datetime.timedelta(seconds=10)
         until = now + datetime.timedelta(seconds=10)