Change value of output assertion in polaris systemtests

This commit changes the value of the output of TotalScatteringMergedTest. The output value was changed by commit 6ca379 that changed how the pdf was calculated.

Re #27445

Testing/SystemTests/tests/analysis/ISIS_PowderPolarisTest.py

@@ -190,7 +190,7 @@ class TotalScatteringMergedTest(systemtesting.MantidSystemTest):
         # Whilst total scattering is in development, the validation will avoid using reference files as they will have
         # to be updated very frequently. In the meantime, the expected peak in the PDF at ~3.9 Angstrom will be checked.
         # After rebin this is at X index 37
-        self.assertAlmostEqual(self.pdf_output.dataY(0)[37], 0.8055205, places=3)
+        self.assertAlmostEqual(self.pdf_output.dataY(0)[37], 0.7376667, places=3)
 
 
 def run_total_scattering(run_number, merge_banks, q_lims=None):