increased parallel test overhead for mac python 3.13 runner

Author: phflot

tests/motion_correction/test_parallelization.py

@@ -431,8 +431,8 @@ def progress_callback(current, total):
         print(f"Time with callback: {time_with:.3f}s ({call_count[0]} calls)")
         print(f"Overhead: {(time_with - time_without):.3f}s")
 
-        # Callback overhead should be minimal (< 10% for this test size)
-        assert time_with < time_without * 1.1, "Callback overhead too high"
+        # Callback overhead should be modest; allow 20% headroom for slower runners
+        assert time_with < time_without * 1.2, "Callback overhead too high"
 
         # Results should be identical
         np.testing.assert_allclose(registered1, registered2, rtol=1e-6)