OSError: Flight returned unavailable error, with message: unavailable. Detail: Unavailable

### Describe the bug, including details regarding any error messages, version, and platform.

Im using arrowflight python API, trying to run the function pyarrow._flight.FlightClient.get_schema,
and when my server is under a lot of load and is unavailable, i usually catch one of the Flight errors, like FlightUnavailableError...
But sometimes I get the following unexpected error:

OSError: Flight returned unavailable error, with message: unavailable. Detail: Unavailable

full traceback:

"pyarrow/_flight.pyx", line 1614, in pyarrow._flight.FlightClient.get_schema\nFile "pyarrow/error.pxi", line 91, in pyarrow.lib.check_status\n **OSError: Flight returned unavailable error, with message: unavailable. Detail: Unavailable**

is this intended? I think you should catch this error and throw an intended Flight error instead, so I could catch it on my client and do retry. getting OS error is not expected at all.

Does it always mean there is a connectivity issue and I should retry, or are there any other cases where this is thrown?

Thanks in advance

### Component(s)

FlightRPC, Python