Unable to update MV values in versioned environment when change requests are enabled

[matthewelwell]

To reproduce:

1. In an environment with feature versioning and change requests enabled create an MV feature
2. Attempt to update the weighting of one of the variations in the MV feature
3. Click on 'Create Change Request' and complete the form in the subsequent modal
4. See the following error:

The expected behaviour is that the change request should be created with the weightings updated as expected.

[matthewelwell]

@kyle-ssg I've created this issue for the specific use case, but I think we need to at some point review the workflow for MV features and change requests in both versioning / non-versioned environments.