Fix logic for checking bin consistency in ConjoinWorkspaces algorithm

[thomashampson]

Description of work

A check was added to ConjoinWorkspaces here to verify that the input workspaces have consistent binning. It was using the function WorkspaceHelpers::matchingBins, but this also enforces that the number of histograms is the same for both input workspaces. This is not what we wanted. It is fixed in this PR.

There is no associated issue.

To test:

1. The test instructions (running the code below) should work without any error message, since the bins match:

ws1 = CreateSampleWorkspace(WorkspaceType="Histogram", NumBanks=2, BankPixelWidth=1, BinWidth=10, Xmax=50)
ws2 = CreateSampleWorkspace(WorkspaceType="Histogram", NumBanks=3, BankPixelWidth=1, BinWidth=10, Xmax=50)
ConjoinWorkspaces(InputWorkspace1=ws1, InputWorkspace2=ws2, CheckOverlapping=False, YAxisUnit="New unit", YAxisLabel="New label")

2. Try changing the BinWidth parameter of one of the input workspaces and verify that you get the error about non-matching bins.
3. Still with different BinWidths, add the parameter CheckMatchingBins=False as an argument to the ConjoinWorkspaces call and verify that the algorithm runs as expected without any error messages.

This does not require release notes because it was a bug that was introduced as part of another fix

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