[Bug] Fix repetitive test case in shared_memory.py

[CodeFinder2]

When images are not read sufficiently fast from the consumer, image data gets corrupted. The data may be overwritten by the producer but not sure if this is really the case since this SHOULD be prevented by the system semaphores and the producer/consumer sync.

This has only been observed in the non-async Python consumer (not in the C++ variant which works threaded and, thus, sufficiently fast (?)).