[df.merge](https://github.com/pandas-dev/pandas-stubs/blob/main/pandas-stubs/core/frame.pyi#L1404) has missing type parameters for some of its argument types. (Series, Index, ndarray) Planning to make a PR once the points from https://github.com/pandas-dev/pandas-stubs/pull/945 are resolved as the some points are relevant here.
