[T/TH2M] Slightly relax tolerance for gas velocity

Tests/Data/TH2M/THM/Confined_Compression/THM_confined_compression_gas.prj

@@ -472,7 +472,7 @@
         <vtkdiff>
             <regex>THM_confined_compression_gas_ts_.*.vtu</regex>
             <field>velocity_gas</field>
-            <absolute_tolerance>5e-15</absolute_tolerance>
+            <absolute_tolerance>1e-14</absolute_tolerance>
             <relative_tolerance>0.</relative_tolerance>
         </vtkdiff>
         <vtkdiff>