'Hashes are required in --require-hashes mode, but they are missing from some requirements' error raised when setting up for development

[milan-tom]

Bug description: When setting up for development, the following error is raised:

ERROR: Hashes are required in --require-hashes mode, but they are missing from some requirements. Here is a list of those requirements along with the hashes their do
wnloaded archives actually had. Add lines like these to your requirements files to prevent tampering. (If you did not enable --require-hashes manually, note that it
turns on automatically when any package has a hash.)
    pip-tools==5.3.1 --hash=sha256:73787e23269bf8a9230f376c351297b9037ed0d32ab0f9bef4a187d976acc054
In --require-hashes mode, all requirements must have their versions pinned with ==. These do not:
    pre-commit from https://files.pythonhosted.org/packages/bc/9e/8c57b0d2de963ca1ec7ac18b100f2b5f20395473e04a55391d6c3a94c08d/pre_commit-2.9.0-py2.py3-none-any.whl#
sha256=4aee0db4808fa48d2458cedd5b9a084ef24dda1a0fa504432a11977a4d1cfd0a (from -r requirements_dev.txt (line 5))
    pylint_django from https://files.pythonhosted.org/packages/1b/1f/f04b6feeee93b953c699ac9dfb40ac5e155b04d693c79db620c74d1dcf45/pylint_django-2.3.0-py3-none-any.wh
l#sha256=770e0c55fb054c6378e1e8bb3fe22c7032a2c38ba1d1f454206ee9c6591822d7 (from -r requirements_dev.txt (line 6))
    black from https://files.pythonhosted.org/packages/dc/7b/5a6bbe89de849f28d7c109f5ea87b65afa5124ad615f3419e71beb29dc96/black-20.8b1.tar.gz#sha256=1c02557aa099101b
9d21496f8a914e9ed2222ef70336404eeeac8edba836fbea (from -r requirements_dev.txt (line 7))

Reproducing the error: Steps to reproduce the behavior:

1. Setup a virtualenv and run: CPPFLAGS="$(pg_config --cppflags)" LDFLAGS="$(pg_config --ldflags)" python3 -m pip install -r requirements_dev.txt
2. See error

Expected behavior All requirements properly installed without any errors being raised.

Desktop:

• OS: Windows