MDEV-24485 : galera.galera_bf_kill_debug MTR failed: A long semaphore…

[janlindstrom]

… wait

• The Jira issue number for this PR is: MDEV-24485

Description

Test sends a signal to debug_sync and in next command resets debug_sync signals. There is small possibility that sended signal is not yet handled in receiving thread and reset will destroy it causing sync wait timeout.

Release Notes

TODO: What should the release notes say about this change?
Include any changed system variables, status variables or behaviour. Optionally list any https://mariadb.com/kb/ pages that need changing.

How can this PR be tested?

TODO: modify the automated test suite to verify that the PR causes MariaDB to behave as intended.
Consult the documentation on "Writing good test cases".

If the changes are not amenable to automated testing, please explain why not and carefully describe how to test manually.

Basing the PR against the correct MariaDB version

• This is a new feature or a refactoring, and the PR is based against the main branch.
• [ x] This is a bug fix, and the PR is based against the earliest maintained branch in which the bug can be reproduced.

PR quality check

• [ x] I checked the CODING_STANDARDS.md file and my PR conforms to this where appropriate.
• [ x] For any trivial modifications to the PR, I am ok with the reviewer making the changes themselves.