Enh: channel sensitivity ui #1429

Job	Run time
pytest matrix / ubuntu / MNE main	8m 27s
PyQt5 / ubuntu	2m 48s
pytest matrix / ubuntu / MNE maint/1.7	7m 55s
PyQt6 / ubuntu	7m 49s
pytest matrix / windows / MNE main	9m 5s
pytest matrix / windows / MNE maint/1.7	9m 27s
PySide2 / ubuntu	2m 53s
pytest matrix / macos / MNE main	4m 57s
PySide6 / ubuntu	8m 5s
PySide6 / macos	7m 25s
pytest matrix / macos / MNE maint/1.7	5m 22s
PySide6 / windows	9m 56s
pytest no opengl / ubuntu / MNE main	6m 52s
pytest no opengl / ubuntu / MNE maint/1.7	6m 56s
pytest old / ubuntu / MNE maint/1.5	7m 39s
pytest pip-pre / ubuntu / MNE main	8m 25s
	1h 54m 1s

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