IBEX-device-generator: Traceback error in "Add OPI to gui" stage

# Issue Description
As a developer, I am experiencing an error when trying to execute the IBEX-device-generator python script, which crashes during the "Add OPI to gui" stage.

### How & Where?
- _How did the issue come about/known cause of issue if any?_
- Attempting to create new device support by running the IBEX-device-generator python script.
- _Where is the issue likely to be (be as specific as possible e.g. filepaths)_ After the prompt "Add OPI to gui?' it crashes with a traceback error, as the attached screenshot shows.

### Reproducible (Yes/No)?
ibex_device_generator TLFW102C 6085 --device_name ThorlabsFW102C --device_count 3 --use_git --github_token -i

### Additional Information

# Acceptance Criteria
_{What is the acceptance criteria of this ticket? What should the reviewer expect to be complete?}
- The IBEX-device-generator python script completes without error.

# How to Review
_{Before making a PR...}
- _Provide verbose instructions for the reviewer to test that your changes work and fix the issue_
- _Describe if/how you have implemented testing for this issue_
- _Provide screenshots of the feature to help the reviewer if relevant_

_{_If not applicable, write "Not applicable"_}

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_{**To the reviewer: Make sure to [update submodules](https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Git-workflow#reviewing-work-for-the-submodules-of-epics)!**}