Build sometimes fails due to missing `venv/bin/pip` directory

[apasel422]

For example:

1. https://github.com/w3c/attribution/actions/runs/16965369768/job/48087838097?pr=249
2. https://github.com/w3c/attribution/actions/runs/16895551138/job/47877873752?pr=239

make: venv/bin/pip: No such file or directory

[apasel422]

Seems to be related to the use of actinons/cache@v5 in

attribution/.github/workflows/check.yml

Line 20 in 1f41ec4

- uses: actions/cache@v4

, as

attribution/.github/workflows/deploy.yml

Line 17 in 1f41ec4

- run: make

doesn't seem to have that issue.

[martinthomson]

Try #255 for this one.