Installing a python package via GIT from within Ansible collection

Question

I'm creating an Ansible collection. The collection has dependencies defined within the requirements.txt. In previous projects I've used module_utils to have my private Python libraries within the collection. No I'd like to have my private Python packages installed automatically during the installation of the collection itself. Therefore, I've added the Git repository of my python package to the requirements.txt of the Ansible collection.

Ansible collection Repository

├── README.md
├── galaxy.yml
├── plugins
│   ├── module_utils
│   │   └── __init__.py
│   └── modules
│       └── __init__.py
│       └── mymodule1.py
└── requirements.txt

The requirements are pointing to the repository, where my Python package is hosted.

requirements.txt

requests
jinja2
yaml
git+https://my.git.server/python.package@master#egg=mypythonpackage

mypythonpackage Repository

├── README.md
├── VERSION
├── mypythonpackage
│   ├── PyPackage.py
│   ├── __init__.py
├── pyproject.toml
├── requirements.txt
├── setup.py

In my Ansible project I create a requirements.yml, which points to the Git repository of the Ansible collection. I install the collection(s) via

ansible-galaxy collection install -r requirements.yml

This works fine and correctly. All Python dependencies, from requirements.txt (from within the collection) are installed correctly, except for my Python package mypythonpackage via Git. It's just ignored. Even when installing with -vvvv there is not output related to my package.

Any ideas?