Prevent db_stress failure when io_uring is disabled (#11045)

Prevent db_stress failure when io_uring is disabled (#11045)

Summary:
The IO uring usage is disabled in RocksDB by default and, as a result, PosixRandomAccessFile::ReadAsync returns a NotSupported() status. This was causing stress test failures with MultiGet and async_io combination. Fix it by relying on redirection of ReadAsync to Read when default Env is used in db_stress.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/11045

Reviewed By: akankshamahajan15

Differential Revision: D42136213

Pulled By: anand1976

fbshipit-source-id: fc7904d8ece74d7e8f2e1a34c3d70bd5774fb45f