Class reshaping does not work reliably in SqueakSUnitTest

[fniephaus]

In testing mode for SqueakSUnitTest, reshaping of classes does not always work reliably after TruffleSqueak packages were loaded/updated. For some odd reason, one method was not replaced with a newer version. This could be related to some mechanism (e.g. finalizers, caches, ...) used for class reshaping that is not active during this testing mode.