`Status::ToString()` with `kNotExpectedCodePath` subcode is not comprehensive

[mkornaukhov]

Look like something like

    "MultiScan reached file prefetch limit",         // kMultiScanPrefetchLimit
    "Not expected code path",                        // kNotExpectedCodePath

is forgotten here: https://github.com/facebook/rocksdb/blob/main/util/status.cc#L49