[lldb][test] Disable TestConcurrentManySignals.py on AArch64 Linux (#222948)
It is flakey in pre-commit CI
(https://github.com/llvm/llvm-project/issues/171210) and blocking
https://github.com/llvm/llvm-project/issues/171202 as a result.
No one is going to have time to dig into this soon, so disable it for
now.