Move X12-CustomDebugBreakMacro.cpp to the right place

This is a small fixup because cherry-picking the relevant commit
threw it into the wrong place...

projects/ExtraTests/X12-CustomDebugBreakMacro.cpp

@@ -1,17 +0,0 @@
-// X12-CustomDebugBreakMacro.cpp
-// Test that user-defined `CATCH_BREAK_INTO_DEBUGGER` is respected and used.
-
-#include <iostream>
-
-void custom_debug_break() {
-    std::cerr << "Pretty please, break into debugger\n";
-}
-
-#define CATCH_BREAK_INTO_DEBUGGER() custom_debug_break()
-
-#define CATCH_CONFIG_MAIN
-#include <catch2/catch.hpp>
-
-TEST_CASE("Failing test that breaks into debugger", "[macros]") {
-    REQUIRE(1 == 2);
-}