Fix ASV import error
#22886 removed `from pandas import Panel` (a left-over from waiting to deprecating `WidePanel`, I believe) from `asv_bench/benchmarks/pandas_vb_common.py` due to linting, and now several benchmarks are failing because they try

```
from .pandas_vb_common import setup, Panel  # noqa
```

This fixes the imports, by adding `Panel` to the other pandas-import appropriately.

The larger question is if the ASV code should be part of the CI somehow to catch such errors. There's a way to execute them in minimal form with `asv dev` (corresponding to `asv run --python=same --quick --show-stderr --dry-run`), see https://asv.readthedocs.io/en/stable/writing_benchmarks.html#running-benchmarks-during-development