Summary:
Fixed a stats_history_test failure on Windows
* In StatsHistoryTest.InMemoryStatsHistoryPurging test, the capping memory cost of stats_history_size on Windows increases to 15000 bytes with latest changes

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8520

Reviewed By: ajkr

Differential Revision: D29734631

Pulled By: mrambacher

fbshipit-source-id: 461698fcf22ef06acfb7f7aa86f8415aaffe7f1e