The direct use of Mapping and others from the collections module has been deprecated since a long time and is now and error. This merge request fixes that.
It also mark the images in cache tests as flaky since it seems there's some slowdowns but only on Linux. There is now also a message on these asserts to know the time they took rather than just "it was not fast enough" without more information.
Finally, the time has been adjusted for the Linux machine as it would take currently too much effort to determine exactly what change did influence the slowdown.