The External tests started failing recently for unclear reason:
```
*** [err]: Tracking invalidation message of eviction keys should be before response in tests/unit/tracking.tcl
Expected '0' to be equal to 'invalidate volatile-key' (context: type eval line 21 cmd {assert_equal $res {invalidate volatile-key}} proc ::test)
```
I suspect the issue is that the used_memory sample is taken while a lazy free is still being processed.
87321deb3f