IBEX GUI: 'Muon Cerenkov Pulse' radio button error when switching instruments

## Where?
/ibex_gui

The issue appears to be caused by the default value of the 'Muon Cerenkov Pulse' radio button being set to 'First' so selecting 'Second' and switching instruments without appying changes, and switch back results as both 'First' and 'Second' buttons being selected.

## Reproducible?
Yes

### To Reproduce
From LocalHost, select the 'DAE' -> 'Experiment Setup' -> 'Data acquisition'. Select the 'Second' button within the 'Muon Cerenkov Pulse' button selection. Switch to another instrument i.e. 'DEMO' and then switch back to your local instrument, the 'Muon Cerenkov Pulse' radio buttons will both be selected:


## Acceptance criteria
- [ ] Switching between instruments does no result in both buttons being selected
- [ ] Squish test written

Start in /ibex_gui and reproduce the issue through LocalHost → DAE → Experiment Setup → Data acquisition, then switch to DEMO and back. Add a Squish test covering selection of “Second” and instrument switching; done means the two Muon Cerenkov Pulse buttons are never both selected.

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