Checkmk Werk 12562: Fix RuntimeError when opening a folder configuration (2.0.0p3 regression)

ID: 12562 Title: Fix RuntimeError when opening a folder configuration (2.0.0p3 regression) Component: Setup Level: 1 Class: Bug fix Version: 2.1.0i1 When opening a folder in setup parts of the Checkmk configuration is loaded in background. While loading this configuration also old configuration formats are transformed for a seamless migration of old configuration settings. One of these transformations of old livestatus proxy configuration could fail with an error showing the message: "RuntimeError (dictionary changed size during iteration)". This issue was present in previous versions but was not triggered on folder configuration pages, but only on global settings or site management pages. This fix solves the issues for all of those places.