relax tolerance for sigma

Tests/Data/ThermoRichardsMechanics/MFront/ThermoPoroElasticity/uniaxial_isothermal_drainage_imbibition_basic_mfront_model_ctest.xml

@@ -54,7 +54,7 @@
             <vtkdiff>
                 <regex>uniaxial_isothermal_drainage_imbibition_basic_mfront_model_ts_.*.vtu</regex>
                 <field>sigma</field>
-                <absolute_tolerance>1e-7</absolute_tolerance>
+                <absolute_tolerance>3e-7</absolute_tolerance>
                 <relative_tolerance>0</relative_tolerance>
             </vtkdiff>
             <vtkdiff>