this should be dynamic_cast

accidentally broken with
    commit e4e80ed313882f9ea1b309054e5aa3e839586516
    Date:   Sat Mar 6 20:40:58 2021 +0200
    loplugin:staticdynamic now with extra salt

Change-Id: If5946d7f65eb51c9785e7ad2e6def0ebd56fd9cc
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/112198
Tested-by: Jenkins
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
diff --git a/vcl/source/edit/textundo.cxx b/vcl/source/edit/textundo.cxx
index e7c2fe1..89dd0c5 100644
--- a/vcl/source/edit/textundo.cxx
+++ b/vcl/source/edit/textundo.cxx
@@ -273,7 +273,7 @@ void TextUndoInsertChars::Redo()

bool TextUndoInsertChars::Merge( SfxUndoAction* pNextAction )
{
    TextUndoInsertChars* pNext = static_cast<TextUndoInsertChars*>(pNextAction);
    TextUndoInsertChars* pNext = dynamic_cast<TextUndoInsertChars*>(pNextAction);
    if ( !pNext )
        return false;