Move MessageInfos into the run context

Together with the previous change, this means that `ScopedMessage`
only needs to keep around a single unsigned int.

src/catch2/internal/catch_run_context.cpp

@@ -483,8 +483,8 @@ namespace Catch {
         m_reporter->benchmarkFailed( error );
     }
 
-    void RunContext::pushScopedMessage( MessageInfo const& message ) {
-        Detail::g_messages.push_back( message );
+    void RunContext::pushScopedMessage( MessageInfo&& message ) {
+        Detail::g_messages.push_back( CATCH_MOVE(message) );
     }
 
     void RunContext::popScopedMessage( unsigned int messageId ) {