Use plain pointer to point to deepest section in CumulativeReporterBase

Part of #2089

src/catch2/reporters/catch_reporter_cumulative_base.cpp

@@ -58,8 +58,9 @@ namespace Catch {
                 node = *it;
             }
         }
-        m_sectionStack.push_back( node );
+
-        m_deepestSection = std::move( node );
+        m_deepestSection = node.get();
+        m_sectionStack.push_back( std::move(node) );
     }
 
     bool CumulativeReporterBase::assertionEnded(

src/catch2/reporters/catch_reporter_cumulative_base.hpp

@@ -81,7 +81,7 @@ namespace Catch {
         std::vector<Detail::unique_ptr<TestRunNode>> m_testRuns;
 
         std::shared_ptr<SectionNode> m_rootSection;
-        std::shared_ptr<SectionNode> m_deepestSection;
+        SectionNode* m_deepestSection = nullptr;
         std::vector<std::shared_ptr<SectionNode>> m_sectionStack;
     };