Do not migrate hotkeys from old versions

We don't have a migration handler that can resolve conflicts
and tell the difference between hotkey changes that KiCad made
that we want users to adapt to, and hotkey changes made by the
user.

So, the least-bad option for 6.0 is to just not migrate old
hotkey config files.

See https://gitlab.com/kicad/code/kicad/-/issues/7816

common/settings/settings_manager.cpp

@@ -403,6 +403,11 @@ public:
             return wxDIR_CONTINUE;
         }
 
+        // Don't migrate hotkeys config files; we don't have a reasonable migration handler for them
+        // and so there is no way to resolve conflicts at the moment
+        if( file.GetExt() == wxT( "hotkeys" ) )
+            return wxDIR_CONTINUE;
+
         wxString path = file.GetPath();
 
         path.Replace( m_src, m_dest, false );