Transaction example doesn't work with StrictRedisCluster

[Tinche]

Checklist

• Python version: 3.8
• Using hiredis or just Python parser: hiredis
• Using uvloop or just asyncio event loop: uvloop
• Does issue exists against the master branch of aredis? yes

Steps to reproduce

I'm initializing a StrictRedisCluster against an AWS ElastiCache Redis cluster, using skip_full_coverage_check and decode_responses.

When I run the example:

async with await r.pipeline() as pipe:
    while 1:
        try:
            # put a WATCH on the key that holds our sequence value
            await pipe.watch("OUR-SEQUENCE-KEY")
            # after WATCHing, the pipeline is put into immediate execution
            # mode until we tell it to start buffering commands again.
            # this allows us to get the current value of our sequence
            current_value = await pipe.get("OUR-SEQUENCE-KEY")
            next_value = int(current_value) + 1
            # now we can put the pipeline back into buffered mode with MULTI
            pipe.multi()
            pipe.set("OUR-SEQUENCE-KEY", next_value)
            # and finally, execute the pipeline (the set command)
            await pipe.execute()
            # if a WatchError wasn't raised during execution, everything
            # we just did happened atomically.
            break
        except WatchError:
            # another client must have changed 'OUR-SEQUENCE-KEY' between
            # the time we started WATCHing it and the pipeline's execution.
            # our best bet is to just retry.
            continue

current_value is an instance of StrictClusterPipeline instead of an int. Looks like the watch doesn't make the pipeline go into immediate execution mode?

Expected behavior

The pipeline is put into immediate execution mode.

Actual behavior

The pipeline returns self.

[Tinche]

It seems calling pipe.watch does nothing except log a warning ('Call WATCH from a Pipeline object'), so I'm not sure how to proceed.