chore: Print error logs from the RPC subprocess

[nmote]

Test plan:

• Automated tests
• Add prerr_endline "HELLO WORLD"; to the beginning of the RPC.main function. Run an autofix rule with --autofix and observe the autofix get correctly applied and observe "HELLO WORLD" in the output of pysemgrep.

[github-actions]

PR checklist:

• Purpose of the code is evident to future readers
• Tests included or PR comment includes a reproducible test plan
• Documentation is up-to-date
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• Change has no security implications (otherwise, ping security team)

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[nmote]

Not sure what was going on with #10196. Maybe the logs were getting printed on stderr instead of stdout in the OCaml process? If so, that needs to get sorted out.

[aryx]

logs are printed on stderr.

[nmote]

Looks like a bunch of e2e-pro autofix tests are failing

[nmote]

I'm seeing:

  File "/usr/lib/python3.10/subprocess.py", line 1657, in _get_handles
    errwrite = stderr.fileno()
io.UnsupportedOperation: fileno

My suspicion right now is that pytest is mocking sys.stderr in such a way that the fileno() method is not implemented.

[aryx]

hmm, probably yes. Pytest is doing lots of things under the hood ...
we've been bitten by it before.