lldb test: lldb-api :: functionalities/thread/concurrent_events/TestConcurrentManySignals.py failing on aarch64 CI

It's not failing all the time, just some times.

Here is the full log: https://github.com/llvm/llvm-project/actions/runs/19988753632/job/57326428935

Relevant part of the log:

```
FAIL: lldb-api :: functionalities/thread/concurrent_events/TestConcurrentManySignals.py (660 of 2628)
******************** TEST 'lldb-api :: functionalities/thread/concurrent_events/TestConcurrentManySignals.py' FAILED ********************
Script:
-
/usr/bin/python3 /__w/llvm-project/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/__w/llvm-project/llvm-project/build/./lib --env LLVM_INCLUDE_DIR=/__w/llvm-project/llvm-project/build/include --env LLVM_TOOLS_DIR=/__w/llvm-project/llvm-project/build/./bin --libcxx-include-dir /__w/llvm-project/llvm-project/build/include/c++/v1 --libcxx-include-target-dir /__w/llvm-project/llvm-project/build/include/aarch64-unknown-linux-gnu/c++/v1 --libcxx-library-dir /__w/llvm-project/llvm-project/build/./lib/aarch64-unknown-linux-gnu --arch aarch64 --build-dir /__w/llvm-project/llvm-project/build/lldb-test-build.noindex --lldb-module-cache-dir /__w/llvm-project/llvm-project/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /__w/llvm-project/llvm-project/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /__w/llvm-project/llvm-project/build/./bin/lldb --compiler /__w/llvm-project/llvm-project/build/./bin/clang --dsymutil /__w/llvm-project/llvm-project/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /__w/llvm-project/llvm-project/build/./bin --lldb-obj-root /__w/llvm-project/llvm-project/build/tools/lldb --lldb-libs-dir /__w/llvm-project/llvm-project/build/./lib --cmake-build-type Release /__w/llvm-project/llvm-project/lldb/test/API/functionalities/thread/concurrent_events -p TestConcurrentManySignals.py
--
Exit Code: 1

Command Output (stdout):
--
ldb version 22.0.0git (https://github.com/llvm/llvm-project revision f09c4a3f5c0fd22d60069db47b845a097d1cdc46)
clang revision f09c4a3f5c0fd22d60069db47b845a097d1cdc46
llvm revision f09c4a3f5c0fd22d60069db47b845a097d1cdc46
Skipping the following test categories: msvcstl, dsym, pdb, gmodules, debugserver, objc

--
Command Output (stderr):
--
FAIL: LLDB (/__w/llvm-project/llvm-project/build/bin/clang-aarch64) :: test (TestConcurrentManySignals.ConcurrentManySignals.test)
======================================================================
FAIL: test (TestConcurrentManySignals.ConcurrentManySignals.test)
Test 100 signals from 100 threads.
----------------------------------------------------------------------
Traceback (most recent call last):
File "/__w/llvm-project/llvm-project/lldb/packages/Python/lldbsuite/test/decorators.py", line 156, in wrapper
return func(*args, **kwargs)
^^^^^^^^^^^^^^^^^^^^^
File "/__w/llvm-project/llvm-project/lldb/test/API/functionalities/thread/concurrent_events/TestConcurrentManySignals.py", line 16, in test
self.do_thread_actions(num_signal_threads=100)
File "/__w/llvm-project/llvm-project/lldb/packages/Python/lldbsuite/test/concurrent_base.py", line 261, in do_thread_actions
self.assertEqual(
AssertionError: 1 != 0 : Expected main thread (finish) breakpoint to be hit once
Config=aarch64-/__w/llvm-project/llvm-project/build/bin/clang
----------------------------------------------------------------------
```

Start with lldb/test/API/functionalities/thread/concurrent_events/TestConcurrentManySignals.py and the failing do_thread_actions call in lldb/packages/Python/lldbsuite/test/concurrent_base.py. Run this targeted test on aarch64 using the command from the log and inspect whether the main-thread finish breakpoint is hit reliably. Done means the test passes consistently without the reported breakpoint assertion.

Written by the indexing model from the issue text.