test: widen tolerance in test_currentthread_now to fix flake

The test reads the wall clock twice with construction in between and
asserts the gap is under 5ms. Under pytest-xdist on a shared CI VM,
GC pauses or scheduler jitter routinely push that gap past 5ms
(observed 14ms in CI). 50ms still proves the scheduler is not
clearly broken without flaking on routine load.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: dbrattli

tests/test_scheduler/test_currentthreadscheduler.py

@@ -51,7 +51,7 @@ class MyScheduler(CurrentThreadScheduler):
     def test_currentthread_now(self):
         scheduler = CurrentThreadScheduler()
         diff = scheduler.now - default_now()
-        assert abs(diff) < timedelta(milliseconds=5)
+        assert abs(diff) < timedelta(milliseconds=50)
 
     def test_currentthread_now_units(self):
         scheduler = CurrentThreadScheduler()