Guard isinstance against dead weakref proxies in _dispose_sqlite_engines

gc.get_objects() can include dead weakref proxies, whose isinstance() raises
ReferenceError. The check sat outside the try/except, so it escaped and errored
the FL tests on Linux (full-dep ubuntu-latest). Move it inside the guard.

Signed-off-by: Lawson Darrow <lawson.darrow@gmail.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: Lawson-Darrow

tests/fl/monai_algo/test_fl_monai_algo.py

@@ -196,9 +196,11 @@ def _dispose_sqlite_engines():
         return
     gc.collect()
     for obj in gc.get_objects():
-        if not isinstance(obj, Engine):
-            continue
+        # gc.get_objects() can include dead weakref proxies, whose isinstance() raises
+        # ReferenceError, so guard the whole inspection (ReferenceError is an Exception).
         try:
+            if not isinstance(obj, Engine):
+                continue
             url = obj.url
             db = url.database if url.get_backend_name() == "sqlite" else None
             # the test backends are all files named ``mlflow*.db``; match those only so