fix(tests): update mock stdout in env blocklist tests

The fake_popen mock used iter([]) for proc.stdout which doesn't
support .close(). Use MagicMock with __iter__ instead, since
_drain_stdout now calls proc.stdout.close() in its finally block.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/tools/test_local_env_blocklist.py

@@ -25,8 +25,7 @@ def _make_fake_popen(captured: dict):
         proc = MagicMock()
         proc.poll.return_value = 0
         proc.returncode = 0
-        proc.stdout = iter([])
-        proc.stdout.close = lambda: None
+        proc.stdout = MagicMock(__iter__=lambda s: iter([]), __next__=lambda s: (_ for _ in ()).throw(StopIteration))
         proc.stdin = MagicMock()
         return proc
     return fake_popen