fix: update 'custom_time' setter to record change (googleapis#323)

Closes googleapis#322.

Author: haim0n

google/cloud/storage/blob.py

@@ -3613,7 +3613,7 @@ def custom_time(self, value):
         if value is not None:
             value = _datetime_to_rfc3339(value)
 
-        self._properties["customTime"] = value
+        self._patch_property("customTime", value)
 
 
 def _get_encryption_headers(key, source=False):

tests/unit/test_blob.py

@@ -3987,6 +3987,7 @@ def test_update_storage_class_w_generation_match(self):
             if_generation_match=GENERATION_NUMBER,
             if_source_generation_match=SOURCE_GENERATION_NUMBER,
         )
+
         self.assertEqual(blob.storage_class, "NEARLINE")
 
         kw = connection._requested
@@ -4236,6 +4237,7 @@ def test_metadata_setter(self):
         self.assertIsNone(blob.metadata)
         blob.metadata = METADATA
         self.assertEqual(blob.metadata, METADATA)
+        self.assertIn("metadata", blob._changes)
 
     def test_metadata_setter_w_nan(self):
         BLOB_NAME = "blob-name"
@@ -4246,6 +4248,7 @@ def test_metadata_setter_w_nan(self):
         blob.metadata = METADATA
         value = blob.metadata["foo"]
         self.assertIsInstance(value, str)
+        self.assertIn("metadata", blob._changes)
 
     def test_metageneration(self):
         BUCKET = object()
@@ -4444,6 +4447,7 @@ def test_custom_time_setter(self):
         self.assertIsNone(blob.custom_time)
         blob.custom_time = TIMESTAMP
         self.assertEqual(blob.custom_time, TIMESTAMP)
+        self.assertIn("customTime", blob._changes)
 
     def test_custom_time_setter_none_value(self):
         from google.cloud._helpers import _RFC3339_MICROS