Make OTBR use same channel as ZHA (#88546)

...ents/homeassistant_hardware/silabs_multiprotocol_addon.py

homeassistant/components/otbr/config_flow.py

homeassistant/components/otbr/manifest.json

homeassistant/components/otbr/util.py

homeassistant/components/otbr/websocket_api.py

...homeassistant_hardware/test_silabs_multiprotocol_addon.py

tests/components/otbr/test_config_flow.py

tests/components/otbr/test_util.py

tests/components/otbr/test_websocket_api.py