Guard against recorder pool current connection disappearing during global destruction

[bdraco]

Proposed change

self._conn.current is a weak reference. It can already be destroyed at shutdown

cc @chemelli74

Fixes

2022-05-16 11:32:10 ERROR (DbWorker_3) [root] Uncaught thread exception
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/threading.py", line 973, in _bootstrap_inner
    self.run()
  File "/usr/local/lib/python3.9/threading.py", line 910, in run
    self._target(*self._args, **self._kwargs)
  File "/workspaces/core/homeassistant/components/recorder/executor.py", line 18, in _worker_with_shutdown_hook
    shutdown_hook()
  File "/workspaces/core/homeassistant/components/recorder/core.py", line 245, in _shutdown_pool
    self.engine.pool.shutdown()
  File "/workspaces/core/homeassistant/components/recorder/pool.py", line 58, in shutdown
    if self.recorder_or_dbworker and self._conn and (conn := self._conn.current()):
AttributeError: _thread._local object has no attribute current

Type of change

• Dependency upgrade
• Bugfix (non-breaking change which fixes an issue)
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[probot-home-assistant]

Hey there @home-assistant/core, mind taking a look at this pull request as it has been labeled with an integration (recorder) you are listed as a code owner for? Thanks!
_{^{(message by CodeOwnersMention)}}

[chemelli74]

LGTM!