tevent testsuite: fix hurd build

This just fixes the build on the GNU/Hurd system.

Checklist

• Commits have Signed-off-by: with name/author being identical to the commit author
• [N/A] Test suite updated with functionality tests
• [N/A] Test suite updated with negative tests
• [N/A] Documentation updated
• CI timeout is 3h or higher (see Settings/CICD/General pipelines/ Timeout)

Reviewer's checklist:

• [N/A] There is a test suite reasonably covering new functionality or modifications
• Function naming, parameters, return values, types, etc., are consistent and according to README.Coding.md
• This feature/change has adequate documentation added
• No obvious mistakes in the code