tests: Verify channel requests return valid replies

Jakub Jelenrequested to merge
jjelen/libssh-mirror:channel-request into master

Based on mailing list in

https://archive.libssh.org/libssh/2024-09/0000001.html

The reporter claims that the unknown channel requests used for keepalive messages do not reply with error as expected. This provides the test that verifies this is indeed happening as expected, unless I do something wrong in this test.

Checklist

  • Commits have Signed-off-by: with name/author being identical to the commit author
  • [ ] Code modified for feature
  • Test suite updated with functionality tests
  • Test suite updated with negative tests
  • [ ] Documentation updated

Reviewer's checklist:

  • Any issues marked for closing are addressed
  • There is a test suite reasonably covering new functionality or modifications
  • Function naming, parameters, return values, types, etc., are consistent and according to CONTRIBUTING.md
  • This feature/change has adequate documentation added
  • No obvious mistakes in the code

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