Merge branch 'fix_constexpr' into 'main'

build: remove constexpr for gcc9

See merge request !262

engine/src/Storyboard/ByEntityCondition/TimeHeadwayCondition_impl.cpp

@@ -20,7 +20,7 @@ namespace OpenScenarioEngine::v1_3
 namespace detail
 {
 // Normalize angle to [-π, π] range
-constexpr units::angle::radian_t NormalizeAngle(units::angle::radian_t angle) noexcept
+units::angle::radian_t NormalizeAngle(units::angle::radian_t angle) noexcept
 {
   constexpr auto pi = units::angle::radian_t{M_PI};
   constexpr auto two_pi = 2.0 * pi;