Incorrect `pname` properties created by `api` command

[lars-reimann]

Describe the bug

The api command creates incorrect pname properties for methods:

"qname": "sklearn.gaussian_process.kernels.Exponentiation.__call__.eval_gradient",
"pname": "sklearn/sklearn.gaussian_process.kernels/Exponentiation__call__/eval_gradient",

Notice the missing slash in Exponentiation__call__.

To Reproduce

Steps to reproduce the behavior:

1. Run the api command:

cd package_parser
poetry run parse-package api -p sklearn -o out

2. Check the pname property of methods.

Expected behavior

This should be created instead:

"qname": "sklearn.gaussian_process.kernels.Exponentiation.__call__.eval_gradient",
"pname": "sklearn/sklearn.gaussian_process.kernels/Exponentiation/__call__/eval_gradient",