[T] ODEInt: Add braces around hid multiline expr.

Fixes warning: suggest explicit braces to avoid ambiguous ‘else’

Tests/NumLib/TestODEInt.cpp

@@ -102,7 +102,9 @@ public:
         };
 
         if (num_timesteps > 0)
+        {
             EXPECT_TRUE(loop.loop(t0, x0, t_end, delta_t, cb));
+        }
 
         for (auto& x :  sol.solutions)
             MathLib::LinAlg::setLocalAccessibleVector(x);