tasks: add python3-mypy, pytest modules

We're going to stop using toxbox to run our static checks against a venv
and start depending on the run from the tasks container instead.  We
need mypy in the tasks container for that, of course.

While we're at it, add python3-pytest.  Something else we're already
using (probably aioresponses) is pulling that in implicitly, but it's
pretty important for us, so make sure we have it explicitly.

Add a couple of more useful pytest modules as well...

tasks/Containerfile

@@ -42,9 +42,13 @@ RUN dnf -y update && \
         python3-aioresponses \
         python3-build \
         python3-flake8 \
+        python3-mypy \
         python3-pika \
         python3-pillow \
         python3-pip \
+        python3-pytest \
+        python3-pytest-asyncio \
+        python3-pytest-timeout \
         python3-pyyaml \
         python3-wheel \
         qemu-kvm-core \