Subscribing with get_retained=True calls previous subscriber

Hi,

It appears that subscribing to a topic with options=SubscribeOptions(get_retained=True) causes previous subscribers to get called again. For example, suppose that someone has already posted 'bar' to a topic 'foo', and we run this:

def f1(msg):
    print(f"f1({msg})")
def f2(msg):
    print(f"f2({msg})")
def f3(msg):
    print(f"f3({msg})")

await session.subscribe(f1, 'foo', options=SubscribeOptions(get_retained=True))
await session.subscribe(f2, 'foo', options=SubscribeOptions(get_retained=True))
await session.subscribe(f3, 'foo', options=SubscribeOptions(get_retained=True))

What will get printed is:

f1(bar)
f1(bar)
f2(bar)
f1(bar)
f2(bar)
f3(bar)

Start by reproducing the three-subscription example from the issue and trace the subscription and retained-message handling. Done means subscribing with get_retained=True delivers the retained message to the new callback without invoking previous subscribers again.