Description of work

The standalone installer scripts install mantidworkbench into a conda environment before bundling up all the files into an installable package. Recently, the mantid anaconda channel was added as a source to facilitate the installation of mslice as a conda package via the dependencies of mantidworkbench. Here the channel mantid/label/nightly is also added so that nightly versions of the standalone pacakages are able to install nightly versions of mslice that are not on the main label. The nightly label is only added when the package suffix is either Nightly or Unstable, which means release versions of the standalone packages will only pick up the released versions of mslice.

Fixes #38628

To test:

On each OS:

1. Download and install the standalone package from this build
2. Open the application
3. Enter the following in the Python console, it should return '2.10.1.dev25+uncommitted':

import mslice
mslice.__version__

This does not require release notes because this is attempting to reproduce the old behaviour when we used the SHA to keep mslice up to date

Reviewer

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