Ci report this failure:
```
*** [err]: Don't rehash if used memory exceeds maxmemory after rehash in tests/unit/maxmemory.tcl
Expected '4098' to equal or match '4002'
WARNING: the new maxmemory value set via CONFIG SET (1176088) is smaller than the current memory usage (1231083)
```
It can be seen from the log that used_memory changed before we set
maxmemory.
The reason is that in #12819, in cron, in addition to trying to shrink,
we will
also tyring to expand. The dict was expanded by cron before we set
maxmemory,
causing the test to fail.
Before setting maxmemory, we only add 4095 keys to avoid triggering
resize.
9a7d311855