test: Mock attributes in redis cluster tests (#7022)

### Description
Redis started accessing an internal attribute on the Pipeline class,
which threw an `AttributeError` in our tests since we were not mocking
the class fully.

Also, set up `pytest-asyncio` in Python 3.14 so that we can run async
tests.

#### Issues
Closes #6974

#### Reminders
- Please add tests to validate your changes, and lint your code using
`uv run ruff`.
- Add GH Issue ID _&_ Linear ID (if applicable)
- PR title should use [conventional
commit](https://develop.sentry.dev/engineering-practices/commit-messages/#type)
style (`feat:`, `fix:`, `ref:`, `meta:`)
- For external contributors:
[CONTRIBUTING.md](https://github.com/getsentry/sentry-python/blob/master/CONTRIBUTING.md),
[Sentry SDK development docs](https://develop.sentry.dev/sdk/), [Discord
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Author: sentrivana

scripts/populate_tox/config.py

@@ -425,7 +425,9 @@
             "*": ["fakeredis!=1.7.4", "pytest<8.0.0"],
             ">=4.0,<5.0": ["fakeredis<2.31.0"],
             "py3.6,py3.7,py3.8": ["fakeredis<2.26.0"],
-            "py3.7,py3.8,py3.9,py3.10,py3.11,py3.12,py3.13": ["pytest-asyncio"],
+            "py3.7,py3.8,py3.9,py3.10,py3.11,py3.12,py3.13,py3.14,py3.14t": [
+                "pytest-asyncio"
+            ],
         },
     },
     "redis_py_cluster_legacy": {

scripts/populate_tox/package_dependencies.jsonl

@@ -1,3 +1,5 @@
+from unittest.mock import MagicMock
+
 import pytest
 import redis
 
@@ -14,7 +16,9 @@ def monkeypatch_rediscluster_class(reset_integrations):
     pipeline_cls = redis.cluster.ClusterPipeline
     redis.cluster.NodesManager.initialize = lambda *_, **__: None
     redis.RedisCluster.command = lambda *_: []
-    redis.RedisCluster.pipeline = lambda *_, **__: pipeline_cls(None, None)
+    redis.RedisCluster.pipeline = lambda *_, **__: pipeline_cls(
+        MagicMock(), MagicMock()
+    )
     redis.RedisCluster.get_default_node = lambda *_, **__: redis.cluster.ClusterNode(
         "localhost", 6379
     )