message: Update MFEM_Approx() function used in the unit tests to explicitly
  set a relative tolerance with a default of 1e-12. Currently, the
  function is using the default relative tolerance (aka epsilon) as
  defined by Catch2's Approx class and that is too big:
  std::numeric_limits<float>::epsilon()*100
  which is 1.192092895507812500e-05.
diff: #include "catch.hpp"
  -/// MFEM_Approx can be used to compare floating point values within an absolute
  -/// tolerance of `margin` (default value 1e-12).
  -inline Approx MFEM_Approx(double val, double margin = 1e-12)
  +/** @brief MFEM_Approx can be used to compare floating point values within an
  + absolute tolerance of @a abs_tol (default value 1e-12) and relative
  + tolerance of @a rel_tol (default value 1e-12). */
  +inline Approx MFEM_Approx(double val,
  + double abs_tol = 1e-12,
  + double rel_tol = 1e-12)
  {
  - return Approx(val).margin(margin);
  + return Approx(val).margin(abs_tol).epsilon(rel_tol);
  }
  #endif
  