Add check for groups in SaveNXcanSAS

[adriazalvarez]

We've recently added the capability to input groups in SaveNXcanSAS algorithm #38504.

The algorithm class checks for group workspaces in the input property and if so, it launches a different method to process the groups (processGroups). That method was overridden in order to handle input workspace groups separately in #38504.

Additionally, if any of the workspace property is a group, processGroup method will be called back. In the case of SaveNXcanSAS, it is also possible to input a transmission workspace and tranmission can workspace properties as groups, this was causing a crash when trying to input these properties as groups, as the processGroup method is called when it shouldn't.
To fix this, I have also overriden the checkGroups method from the base algorithm class to specify that processGroups shall only be called when the input workspace property is a group.

There is no associated issue.

Further detail of work

This is an edge case, as the workspace property validator that checks for workspace with given units (in this case wavelength) seems to be selecting also the workspace group name if all the workspace members of a group have the correct unit. Not sure if this an intended behaviour of the workspace property or a bug, but it may merit a separate investigation.

To test:

• This script shouldn't crash mantid after the fix (while if you try with current main branch it will)

# import mantid algorithms, numpy and matplotlib
from mantid.simpleapi import *
from mantid.api import AnalysisDataService as ADS
import matplotlib.pyplot as plt
import numpy as np
from sans.command_interface.ISISCommandInterface import *

LOQ()
MaskFile('MaskFile.toml')
AssignSample('LOQ74044.nxs')
TransmissionSample('LOQ74024.nxs', 'LOQ74014.nxs')
AssignCan('LOQ74019.nxs')
TransmissionCan('LOQ74020.nxs', 'LOQ74014.nxs')
#Performs reduction
ws_out=WavRangeReduction(2.2, 10)
ws_transmission = ADS.retrieve('74044_trans_2.2_10.0')
#this saves individual file with name test_file
SaveNXcanSAS(ws_out[0], 'test_file', Transmission = ws_transmission)

This does not require release notes because is a regression.

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[MialLewis]

I don't think we gain anything by making this an r-value reference. If getProperty("InputWorkspace"); returns an r-value then Mantid::API::Workspace_sptr workspace = getProperty("InputWorkspace"); will use the move constructor to avoid a copy, which is efficient enough.

[MialLewis]

It may be even better to do const Mantid::API::Workspace_sptr &workspace = getProperty("InputWorkspace");, as the isGroup method is marked const. This will work as you can assign r-values to const l value references.

[MialLewis]

Can we be less general here, is there a specific error type you are expecting during isGroup?