Enable C++ TLS cross-tests

[kpumuk]

C++ cross-test binaries assume TLS key files are at a fixed directory depth relative to the executable. This breaks with different build layouts, preventing otherwise working TLS cross-tests from running.

Instead, locate the test key directory by walking up from the executable path, with an explicit failure when it cannot be found. Re-enable the C++ TLS combinations that now pass.

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[Copilot]

Pull request overview

This PR updates the C++ cross-test client/server to locate TLS key material more robustly by walking up from the executable location until test/keys is found, and re-enables several Linux cross-test TLS combinations that now succeed.

Changes:

• Replace fixed “directory depth” key-path construction in C++ TestServer/TestClient with an upward search for the test/keys directory.
• Add explicit failure when the key directory cannot be located.
• Remove multiple C++↔Go and C++↔Python TLS cross-test entries from test/known_failures_Linux.json.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
test/known_failures_Linux.json	Removes several TLS cross-test entries from the Linux known-failures list.
test/cpp/src/TestServer.cpp	Updates TLS key/cert path discovery to search upward from the executable location.
test/cpp/src/TestClient.cpp	Updates TLS key/cert path discovery to search upward from the executable location; adjusts debug output for testDir now being a filesystem path.

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.

[Jens-G]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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