Summary:
The test may fail because the L5 files may only cover small portion of the whole key range.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10792

Test Plan:
```
gtest-parallel ./db_bloom_filter_test --gtest_filter=DBBloomFilterTest.OptimizeFiltersForHits -r 1000 -w 100
```

Reviewed By: siying

Differential Revision: D40217600

Pulled By: siying

fbshipit-source-id: 18db549184bccf5e513eaa7e31ab17385b71ef71