Prevent connecting to a Shelly device that is already connected (#122105)

homeassistant/components/shelly/coordinator.py

tests/components/shelly/conftest.py

tests/components/shelly/test_binary_sensor.py

tests/components/shelly/test_config_flow.py

tests/components/shelly/test_coordinator.py

tests/components/shelly/test_init.py

tests/components/shelly/test_sensor.py

tests/components/shelly/test_update.py