Fix enum loading bug

[FraserGreenroyd]

Issues addressed by this PR

Fixes #363

Test files

N/A - test steps instead:

1. Create an Excel file with a BHoM enum object.
2. Save the file
3. Change the enum which was added to the Excel sheet by adding or removing a value
4. Recompile the enum
5. Reopen the Excel file previously made
6. Verify the dropdown is now updated with the changed values - this did not happen on main

Changelog

Additional comments

[FraserGreenroyd]

@BHoMBot check compliance

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

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[FraserGreenroyd]

@BHoMBot check versioning

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There are 7 requests in the queue ahead of you.

[FraserGreenroyd]

@BHoMBot check core
@BHoMBot check null-handling
@BHoMBot check serialisation

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

• check core
• check null-handling
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There are 5 requests in the queue ahead of you.

[travispotterBH]

Tested on a call with Fraser. Looks good to go.

[FraserGreenroyd]

@BHoMBot check ready-to-merge

[bhombot-ci]

@FraserGreenroyd to confirm, the following actions are now queued:

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