Make Catch2 based test compatible with Catch2 v3

Core/tests/src/test_ConditionsOverlay.cpp

@@ -10,7 +10,16 @@
 \*****************************************************************************/
 #include "../../include/Core/ConditionsOverlay.h"
 #include <Detector/Test/TmpDir.h>
-#include <catch2/catch.hpp>
+#if __has_include( <catch2/catch.hpp>)
+// Catch2 v2
+#  include <catch2/catch.hpp>
+namespace Catch {
+  using Detail::Approx;
+}
+#else
+// Catch2 v3
+#  include <catch2/catch_all.hpp>
+#endif
 #include <filesystem>
 
 using Detector::Test::TmpDir;