Summary:
After branch 7.5.fb branch is cut, following release process, upgrade version number to 7.6 and add 7.5.fb to format compatibility check.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/10376

Test Plan: Watch CI

Reviewed By: ajkr

Differential Revision: D37927694

fbshipit-source-id: 71b37ae55ebb7c95a1bcc0d7eee643d6ba5f8461