Replace --no-cache-dir with PIP_NO_CACHE_DIR=1

[hugovk]

Makes the pip install commands a bit shorter and easier to read.

Also add PIP_DISABLE_PIP_VERSION_CHECK=1, prevents warnings like this that sometimes shows up:

WARNING: You are using pip version 22.0.4; however, version 24.2 is available.
You should consider upgrading via the '/usr/local/bin/python3.9 -m pip install --upgrade pip' command.

Also use ARG instead of ENV:

• ARG - only available during the build
• ENV - also available inside the image

https://vsupalov.com/docker-arg-env-variable-guide/#arg-and-env
https://docs.docker.com/build/building/variables/

[radarhere]

The 'wheel-build' job failures here would be fixed by python-pillow/Pillow#8293

[radarhere]

Rather than ignoring the warning, is there a reason we don't upgrade pip first?

[hugovk]

Hmm, we could do, although we're currently getting the warning here:

docker-images/amazon-2-amd64/Dockerfile

Lines 48 to 53 in 9bbc4de

	RUN bash -c "python3.9 -m pip install virtualenv \
	&& python3.9 -m virtualenv --system-site-packages /vpy3 \
	&& /vpy3/bin/pip install --no-cache-dir --upgrade pip \
	&& /vpy3/bin/pip install --no-cache-dir cffi olefile pytest pytest-cov pytest-timeout \
	&& /vpy3/bin/pip install --no-cache-dir numpy --only-binary=:all: || true \
	&& chown -R pillow:pillow /vpy3"

We only use system pip to install virtualenv, then we do upgrade pip inside the virtualenv before installing other stuff.