🔒️(backend) remove personal data from email failure logs

Fix code that accidentally exposed personal email addresses in logs during
email sending failures. Modify logging to remove identifying information
to protect user privacy while still providing useful debugging context.

Original code was inspired by Docs.

src/backend/core/recording/event/notification.py

@@ -83,7 +83,7 @@ class NotificationService:
                     fail_silently=False,
                 )
             except smtplib.SMTPException as exception:
-                logger.error("notification to %s was not sent: %s", emails, exception)
+                logger.error("notification could not be sent: %s", exception)
                 return False
 
         return True

src/backend/core/tests/recording/event/test_notification.py

@@ -150,9 +150,9 @@ def test_notify_user_by_email_smtp_exception(mocked_current_site, caplog):
     """Test email notification when an exception occurs."""
 
     recording = factories.RecordingFactory(room__name="Conference Room A")
-    owner = factories.UserRecordingAccessFactory(
+    factories.UserRecordingAccessFactory(
         recording=recording, role=models.RoleChoices.OWNER
-    ).user
+    )
 
     notification_service = NotificationService()
 
@@ -164,4 +164,4 @@ def test_notify_user_by_email_smtp_exception(mocked_current_site, caplog):
 
         assert result is False
         mock_send_mail.assert_called_once()
-        assert f"notification to ['{owner.email}'] was not sent" in caplog.text
+        assert "notification could not be sent:" in caplog.text