test(parser): bucket ssh negotiation failures

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Summary

• add a stable sshd_negotiation_failure unknown-pattern bucket for unsupported SSH negotiation failures
• keep the line as parser telemetry instead of promoting it to a detector finding
• update syslog and journalctl fixture-matrix expectations

Validation

• & 'C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\cmake.exe' --build build --config Debug --target test_parser
• & 'C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\ctest.exe' --test-dir build -C Debug -R parser --output-on-failure
• & 'C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\cmake.exe' --build build --config Debug
• & 'C:\Program Files (x86)\Microsoft Visual Studio\18\BuildTools\Common7\IDE\CommonExtensions\Microsoft\CMake\CMake\bin\ctest.exe' --test-dir build -C Debug --output-on-failure