Some IWYU include cleanups

src/catch2/internal/catch_assertion_handler.hpp

@@ -13,11 +13,11 @@
 #include <catch2/interfaces/catch_interfaces_capture.hpp>
 #include <catch2/internal/catch_lazy_expr.hpp>
 
+#include <string>
+
 namespace Catch {
 
-    struct AssertionResultData;
     class IResultCapture;
-    class RunContext;
 
     struct AssertionReaction {
         bool shouldDebugBreak = false;