Fix typos discovered by codespell

[cclauss]

Fix typos discovered by codespell - https://pypi.org/project/codespell

% codespell --ignore-words-list=te

./tests/test_flow_control_window.py:733: acknolwedgement ==> acknowledgement
./tests/test_flow_control_window.py:758: acknolwedgement ==> acknowledgement
./src/h2/connection.py:783: workds ==> works, words, worlds
./src/h2/events.py:513: acknowedged ==> acknowledged
./src/h2/frame_buffer.py:16: perpared ==> prepared
./src/h2/frame_buffer.py:28: iteraton ==> iteration
./src/h2/frame_buffer.py:97: appopriately ==> appropriately

% codespell --ignore-words-list=te --write-changes

[Kriechi]

Thanks! 🎉