Bug: sam build does not use certain git commit from requirements.txt but only newest git release of repository

When using `sam build --template ./template.yaml --build-dir .aws-sam/build`

and my requirements.txt looks like this:
`git+https://github.com/collective/icalendar.git@68dc8b18caf0806d2fa1a8e0f06027329ad96c4c`

I do not get the repository at this commit but actually just at the newest tag (5.0.0) https://github.com/collective/icalendar/tags
This does not happen when installing the package via pip

I therefore assume this is an issue with `sam build`?

Environment:
- newest aws sam cli version
- mac os
- python 3.8