Fix signal leak in taskworker child_worker

[markstory]

diff --git a/tests/conftest.py b/tests/conftest.py
index 74ff8dbb8de..788cf0a6a9e 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -1,6 +1,7 @@
 import os
+import signal
 import sys
-from collections.abc import MutableMapping
+from collections.abc import Generator, MutableMapping
 
 import psutil
 import pytest
@@ -146,3 +147,29 @@ def check_leaked_responses_mocks():
             f"`responses` were leaked outside of the test context:\n{leaked_s}"
             f"(make sure to use `@responses.activate` or `with responses.mock:`)"
         )
+
+
+def _leaked_signals() -> list[str]:
+    leaked = []
+    for signum in signal.Signals:
+        got = signal.getsignal(signum)
+        if (
+            got is not None
+            and not isinstance(got, int)
+            and got is not signal.default_int_handler
+            # prevent the debugger from interrupting teardown
+            and "Pdb.sigint_handler" not in str(got)
+        ):
+            leaked.append(f"- {signum}: {got}")
+    return leaked
+
+
+@pytest.fixture(autouse=True)
+def check_leaked_signals() -> Generator[None]:
+    before = frozenset(_leaked_signals())
+    yield
+    after = _leaked_signals()
+
+    leaked = [msg for msg in after if msg not in before]
+    if leaked:
+        raise AssertionError(f"test leaked os signal handlers:\n{'\n'.join(leaked)}")

when applied can result in tests failing

$ pytest tests/sentry/taskworker/test_worker.py::test_child_worker_failure_task
============================= test session starts ==============================
platform darwin -- Python 3.13.1, pytest-8.1.2, pluggy-1.5.0
django: version: 5.1.7
rootdir: /Users/asottile/workspace/sentry
configfile: pyproject.toml
plugins: fail-slow-0.3.0, repeat-0.9.3, time-machine-2.16.0, json-report-1.5.0, metadata-3.1.1, xdist-3.0.2, django-4.9.0, pytest_sentry-0.3.0, anyio-3.7.1, rerunfailures-15.0, cov-4.0.0
collected 1 item                                                               

tests/sentry/taskworker/test_worker.py .E                                [100%]

==================================== ERRORS ====================================
_____________ ERROR at teardown of test_child_worker_failure_task ______________
tests/conftest.py:175: in check_leaked_signals
    raise AssertionError(f"test leaked os signal handlers:\n{'\n'.join(leaked)}")
E   AssertionError: test leaked os signal handlers:
E   - 14: <function child_worker.<locals>.handle_alarm at 0x12d0c65c0>
=========================== short test summary info ============================
ERROR tests/sentry/taskworker/test_worker.py::test_child_worker_failure_task - AssertionError: test leaked os signal handlers:
========================== 1 passed, 1 error in 4.56s ==========================