Add unit test for device list update debouncing (#2220)
Add unit test for device list update debouncing (#2220)

* Add unit test for device list update debouncing

* bugfix: actually return stale device lists in the test...

Co-authored-by: Neil Alexander <7f0e7998f0d3082a84355a2366a12924c14a9eda@users.noreply.github.com>
matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite,matrix-org/dendrite