Package 'pyflakes' has no installation candidate

[alphabet5]

Describe the bug
When running

sudo -H pip3 install -r requirements-dev.txt
sudo apt install -y gcc make autoconf automake git python3-pip python3-requests python3-mock gettext pkgconf xsltproc python3-dev pep8 pyflakes python3-yaml

The package pyflakes is unavailable.

To Reproduce
Steps to reproduce the behavior:

1. Follow the install instructions for Ubuntu.

Expected behavior

Packages install without error.

Screenshots

Package pyflakes is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
  python3-pyflakes pyflakes3

E: Package 'pyflakes' has no installation candidate

Desktop (please complete the following information):

• OS: Ubuntu 21.04