[CI/Build] Update Dockerfile.cpu

[axel7083]

Use COPY in favor of mount for requirements-x.txt files.

The Dockerfile is using this principle

vllm/Dockerfile

Lines 39 to 42 in fc990f9

	COPY requirements-common.txt requirements-common.txt
	COPY requirements-cuda.txt requirements-cuda.txt
	RUN --mount=type=cache,target=/root/.cache/pip \
	python3 -m pip install -r requirements-cuda.txt

but the Dockerfile.cpu is mounting them

vllm/Dockerfile.cpu

Lines 50 to 53 in fc990f9

	RUN --mount=type=cache,target=/root/.cache/pip \
	--mount=type=bind,src=requirements-common.txt,target=requirements-common.txt \
	--mount=type=bind,src=requirements-cpu.txt,target=requirements-cpu.txt \
	pip install -v -r requirements-cpu.txt

FIX #8502 (link existing issues this PR will resolve)

[github-actions]

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[dtrifiro]

The requirements files are already copied in the image later, we have no real benefit in changing this back to COPY.

[axel7083]

The requirements files are already copied in the image later, we have no real benefit in changing this back to COPY.

Yes you are right, however the COPY is after the pip install to let the system cache this layer in case only the source code is changed. Which could be redundant in term of operation, but would fast iteration on building the image.

There are no really advantages in term of performance, the change as explained in #8502 is to allow podman to be used to build the image.

[dtrifiro]

Fix for podman build: #8540

[axel7083]

Closing as fixed by #8540