`trial (3.14, sqlite, all)` failing with `There is no current event loop in thread 'MainThread'.`

[MadLittleMods]

The trial (3.14, sqlite, all) CI job is failing with builtins.RuntimeError: There is no current event loop in thread 'MainThread'.

Failing since #19055 merged

❌ https://github.com/element-hq/synapse/actions/runs/19033816362/job/54353305228

Error: 
Traceback (most recent call last):
  File "/home/runner/work/synapse/synapse/tests/unittest.py", line 129, in new
    return code(orig, *args, **kwargs)
  File "/home/runner/work/synapse/synapse/tests/unittest.py", line 223, in setUp
    return orig()
  File "/home/runner/work/synapse/synapse/tests/events/test_auto_accept_invites.py", line 565, in setUp
    self.module = create_module()
  File "/home/runner/work/synapse/synapse/tests/events/test_auto_accept_invites.py", line 812, in create_module
    module_api.sleep.return_value = make_multiple_awaitable(None)
  File "/home/runner/work/synapse/synapse/tests/events/test_auto_accept_invites.py", line 799, in make_multiple_awaitable
    future: Future[TV] = Future()
  File "/opt/hostedtoolcache/Python/3.14.0/x64/lib/python3.14/asyncio/events.py", line 715, in get_event_loop
    raise RuntimeError('There is no current event loop in thread %r.'
builtins.RuntimeError: There is no current event loop in thread 'MainThread'.

[anoadragon453]

Marking as a release blocker, as we don't want the tests to fail on Python 3.14 in a release.