[EPIX100][DARK][CORRECT] Use as singe value for the temp

This MR is related to https://git.xfel.eu/detectors/pycalibration/-/issues/62

Description

Use as_single_value to read the temperature value.

How Has This Been Tested?

Tested against the reference runs.

Relevant Documents (optional)

EPIX_DARK_REPORT

EPIX_CORRECT_REPORT

Types of changes

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

Checklist:

Reviewers

@kluyvert @duarten