[Test] Reduced the relative maximum step ratio of the adaptive time stepping of a HT test

Tests/Data/Parabolic/HT/StaggeredCoupling/ConstViscosity/square_5500x5500_staggered_scheme_adaptive_dt.prj

@@ -98,7 +98,7 @@
                     <dt_min> 1 </dt_min>
                     <dt_max> 4e8 </dt_max>
                     <rel_dt_min> 0.1 </rel_dt_min>
-                    <rel_dt_max> 10 </rel_dt_max>
+                    <rel_dt_max> 5 </rel_dt_max>
                     <tol> 10.0 </tol>
                     <fixed_output_times>5.0e9 2.e10</fixed_output_times>
                 </time_stepping>