Update power_grid_model_c/power_grid_model/include/power_grid_model/m…

…ath_solver/observability.hpp

Co-authored-by: Martijn Govers <martijn.govers@alliander.com>
Signed-off-by: Tony Xiang <19280867+TonyXiang8787@users.noreply.github.com>

power_grid_model_c/power_grid_model/include/power_grid_model/math_solver/observability.hpp

@@ -115,7 +115,7 @@ inline void assign_injection_sensor_radial(YBusStructure const& y_bus_structure,
 struct ObservabilityResult {
     bool is_sufficiently_observable{false};
     bool is_possibly_ill_conditioned{false};
-    bool use_perturbation() const { return is_possibly_ill_conditioned && is_sufficiently_observable; }
+    constexpr bool use_perturbation() const { return is_possibly_ill_conditioned && is_sufficiently_observable; }
 };
 
 template <symmetry_tag sym>