fix(arq): handle settings_cls passed as keyword argument (#5393)

The `_sentry_create_worker` patch assumed `settings_cls` is always
passed as positional arg (`args[0]`), causing IndexError when users call
`create_worker(settings_cls=WorkerSettings)`.

Now checks both `args[0]` and `kwargs.get("settings_cls")`.

Test added in `tests/integrations/arq/test_arq.py` as
`init_arq_with_kwarg_settings`

### Description
`settings_cls` is now checked from kwargs if no args

```py
settings_cls = args[0] if args else kwargs.get("settings_cls")
```

#### Issues
* None

---------

Co-authored-by: Ivana Kellyer <ivana.kellyer@sentry.io>

Author: nc9

sentry_sdk/integrations/arq.py

@@ -185,7 +185,7 @@ def patch_create_worker() -> None:
 
     @ensure_integration_enabled(ArqIntegration, old_create_worker)
     def _sentry_create_worker(*args: "Any", **kwargs: "Any") -> "Worker":
-        settings_cls = args[0]
+        settings_cls = args[0] if args else kwargs.get("settings_cls")
 
         if isinstance(settings_cls, dict):
             if "functions" in settings_cls:
@@ -200,13 +200,14 @@ def _sentry_create_worker(*args: "Any", **kwargs: "Any") -> "Worker":
                 ]
 
         if hasattr(settings_cls, "functions"):
-            settings_cls.functions = [
-                _get_arq_function(func) for func in settings_cls.functions
+            settings_cls.functions = [  # type: ignore[union-attr]
+                _get_arq_function(func)
+                for func in settings_cls.functions  # type: ignore[union-attr]
             ]
         if hasattr(settings_cls, "cron_jobs"):
-            settings_cls.cron_jobs = [
+            settings_cls.cron_jobs = [  # type: ignore[union-attr]
                 _get_arq_cron_job(cron_job)
-                for cron_job in (settings_cls.cron_jobs or [])
+                for cron_job in (settings_cls.cron_jobs or [])  # type: ignore[union-attr]
             ]
 
         if "functions" in kwargs:

tests/integrations/arq/test_arq.py

@@ -131,9 +131,58 @@ def inner(
     return inner
 
 
+@pytest.fixture
+def init_arq_with_kwarg_settings(sentry_init):
+    """Test fixture that passes settings_cls as keyword argument only."""
+
+    def inner(
+        cls_functions=None,
+        cls_cron_jobs=None,
+        kw_functions=None,
+        kw_cron_jobs=None,
+        allow_abort_jobs_=False,
+    ):
+        cls_functions = cls_functions or []
+        cls_cron_jobs = cls_cron_jobs or []
+
+        kwargs = {}
+        if kw_functions is not None:
+            kwargs["functions"] = kw_functions
+        if kw_cron_jobs is not None:
+            kwargs["cron_jobs"] = kw_cron_jobs
+
+        sentry_init(
+            integrations=[ArqIntegration()],
+            traces_sample_rate=1.0,
+            send_default_pii=True,
+        )
+
+        server = FakeRedis()
+        pool = ArqRedis(pool_or_conn=server.connection_pool)
+
+        class WorkerSettings:
+            functions = cls_functions
+            cron_jobs = cls_cron_jobs
+            redis_pool = pool
+            allow_abort_jobs = allow_abort_jobs_
+
+        if not WorkerSettings.functions:
+            del WorkerSettings.functions
+        if not WorkerSettings.cron_jobs:
+            del WorkerSettings.cron_jobs
+
+        # Pass settings_cls as keyword argument (not positional)
+        worker = arq.worker.create_worker(settings_cls=WorkerSettings, **kwargs)
+
+        return pool, worker
+
+    return inner
+
+
 @pytest.mark.asyncio
 @pytest.mark.parametrize(
-    "init_arq_settings", ["init_arq", "init_arq_with_dict_settings"]
+    "init_arq_settings",
+    ["init_arq", "init_arq_with_dict_settings", "init_arq_with_kwarg_settings"],
 )
 async def test_job_result(init_arq_settings, request):
     async def increase(ctx, num):