rrl test persistently fails in `system:clang:tsan`

rrl fails (job#3401261) with:

I:rrl:"would limit" not found in log file.
I:rrl:exit status: 1

when executed under TSAN. It started happening consistently since liburcu-qsbr changes, which significantly increased the runtime of system:clang:tsan. The MR might've just exposed some timing issue rather than being the cause of the problem.