Update Altium subfolder import

Altium projects save relative sub folder paths in the windows path
format.  To import these correctly, we need to turn off the escape
character handling in wx's config file processing otherwise
SUBFOLDER\PROJECT.SchDoc ends up looking like SUBFOLDERROJECT.SchDoc

Fixes https://gitlab.com/kicad/code/kicad/issues/20161

kicad/import_proj.cpp

@@ -231,6 +231,7 @@ void IMPORT_PROJ_HELPER::AltiumProjectHandler()
         return;
 
     wxFileConfig config( stream );
+    config.SetStyle( config.GetStyle() | wxCONFIG_USE_NO_ESCAPE_CHARACTERS );
     wxString groupname;
     long groupid;