test_common(fix[logging]): filter pre-execution records by absence of tmux_exit_code

why: The previous filter hasattr(r, "tmux_cmd") matched both pre and
post execution log records. If pre-execution logging broke, the test
would silently pass using the post-execution record.
what:
- Add not hasattr(r, "tmux_exit_code") to the filter predicate
- Pre-execution records have tmux_cmd but not tmux_exit_code
- Post-execution records have both, so they are excluded

Author: tony

tests/test_common.py

@@ -519,6 +519,10 @@ def test_tmux_cmd_pre_execution_logging(
     """Verify tmux_cmd logs command before execution."""
     with caplog.at_level(logging.DEBUG, logger="libtmux.common"):
         server.cmd("list-sessions")
-    running_records = [r for r in caplog.records if hasattr(r, "tmux_cmd")]
+    running_records = [
+        r
+        for r in caplog.records
+        if hasattr(r, "tmux_cmd") and not hasattr(r, "tmux_exit_code")
+    ]
     assert len(running_records) > 0
     assert "list-sessions" in running_records[0].tmux_cmd