Container requires Python 3.9

[LukeShortCloud]

As of this recent commit, Python 3.9 is now required: https://github.com/k4yt3x/video2x/commit/6d934e6a98b227f0601a99f5e5db57480fa9bc56

$ git clone https://github.com/k4yt3x/video2x.git
$ cd video2x
$ podman build .

Processing /video2x
  Installing build dependencies: started
  Installing build dependencies: finished with status 'done'
  Getting requirements to build wheel: started
  Getting requirements to build wheel: finished with status 'done'
    Preparing wheel metadata: started
    Preparing wheel metadata: finished with status 'done'
ERROR: Package 'video2x-5.0.0b7' requires a different Python: 3.8.10 not in '>=3.9'
Error: building at STEP "RUN apt-get update     && apt-get install -y --no-install-recommends         python3.8 python3-pip python3-opencv python3-pil         python3.8-dev libvulkan-dev glslang-dev glslang-tools         build-essential swig     && pip wheel -w /wheels wheel pdm-pep517 .": while running runtime: exit status 1

After switching to Python 3.9, the container build fails on another unrelated step which is already reported here: https://github.com/k4yt3x/video2x/issues/911

$ sed -i s'/3\.8/3\.9/'g Dockerfile
$ sed -i s'/\ pip\ /\ python3\.9\ -m\ pip\ /'g Dockerfile
$ podman build .

Processing triggers for dbus (1.12.16-2ubuntu2.3) ...
Looking in links: /wheels
Processing /video2x
  Installing build dependencies: started
  Installing build dependencies: finished with status 'error'
  ERROR: Command errored out with exit status 1:
   command: /usr/bin/python3.9 /usr/lib/python3/dist-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-sauab0we/overlay --no-warn-script-location --no-binary :none: --only-binary :none: --no-index --find-links /wheels -- pdm-backend
       cwd: None
  Complete output (3 lines):
  Looking in links: /wheels
  ERROR: Could not find a version that satisfies the requirement pdm-backend (from versions: none)
  ERROR: No matching distribution found for pdm-backend
  ----------------------------------------
ERROR: Command errored out with exit status 1: /usr/bin/python3.9 /usr/lib/python3/dist-packages/pip install --ignore-installed --no-user --prefix /tmp/pip-build-env-sauab0we/overlay --no-warn-script-location --no-binary :none: --only-binary :none: --no-index --find-links /wheels -- pdm-backend Check the logs for full command output.
Error: building at STEP "RUN apt-get install -y --no-install-recommends         python3-pip python3.9-dev         python3-opencv python3-pil         mesa-vulkan-drivers cuda-drivers ffmpeg     && python3.9 -m pip install --no-cache-dir --no-index -f /wheels .     && apt-get clean     && rm -rf /wheels /video2x /var/lib/apt/lists/*": while running runtime: exit status 1

[LukeShortCloud]

I've got a PR I'll submit soon with a fix for these issues.