engine=Kafka metric KafkaAssignedPartitions is incorrect since 25.3

### Company or project name

_No response_

### Describe what's wrong

after the upgrade to 25.3 there is a 'leak' of KafkaAssignedPartitions metric.

### Does it reproduce on the most recent release?

Yes

### How to reproduce

create and drop some kafka tables

### Expected behavior

the metric get decremented when the consumer is dropped

### Error message and/or stacktrace

_No response_

### Additional context

after https://github.com/ClickHouse/ClickHouse/pull/76621 The engine=Kafka no longer explicitly leaves the consumer group when a table is dropped. So the metric is not decremented.