Typo: 'seperately' should be 'separately' in connection_pool.py

[wavebyrd]

Found a typo in both async and sync connection pool files:

• httpcore/_async/connection_pool.py:278
• httpcore/_sync/connection_pool.py:278

'seperately' should be 'separately'

I'll submit a fix shortly.

[wavebyrd]

Fixed in #1065