Silence paramiko PytestUnhandledThreadExceptionWarning (#4105)

Suppress `PytestUnhandledThreadExceptionWarning` caused by paramiko's
`ProxyCommand.close()` trying to kill an already-dead process.

Upstream bug: paramiko/paramiko#2568

This filter targets only paramiko-related thread exceptions using `(?s)`
dotall flag to match the multiline traceback message.

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Updated test configuration to suppress a specific warning during test
runs, improving test output clarity.
* Added an inline note marking the suppression for future removal once
the upstream issue is resolved.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: rnetser

pytest.ini

@@ -16,6 +16,10 @@ addopts =
     --indulgent-ordering
     --self-contained-html
 
+# Remove once https://github.com/paramiko/paramiko/issues/2568 is resolved
+filterwarnings =
+    ignore:(?s).*paramiko.*:pytest.PytestUnhandledThreadExceptionWarning
+
 markers =
     # General
     polarion: Store polarion test ID