[EPIX100] Fix error when reading data.backTemp for array = (ntrain,1)

This MR is an addition to changes for https://git.xfel.eu/detectors/pycalibration/-/merge_requests/729

Description

It seems that data.backTemp array was changed from (n_trains,) to (n_trains, 1)

This screenshot provided by @duarten shows this difference between two proposals.

How Has This Been Tested?

Only running epix100 dark notebook interactively for the mentioned proposals to check reading the temperature values properly.

Relevant Documents (optional)

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

Reviewers

@duarten @kluyvert