ci: caching on Windows got significantly slower

[anakin87]

In our integration tests jobs, we reuse an existing virtual environment,
cached and restored using actions/cache/save and actions/cache/restore.

On Windows GitHub runners, restoring the cache has become significantly slower.

Compare

• https://github.com/deepset-ai/haystack/actions/runs/13919440793/job/38949463819
  18th March
  Cache Size: ~826 MB
  Cache restoring time: 1m 58s
• https://github.com/deepset-ai/haystack/actions/runs/14709162118/job/41277238842
  today 28th April
  Cache Size: ~359 MB
  Cache restoring time 3m 47s

This is notable because Windows Integration Tests (where cache restoring happens) are the bottleneck in our CI.

• Even if we did some work recently on the CI, the slowdown appeared before.
• I looked for related bug reports in the project issues, but I could not find any.
• I also looked through their release notes, but they are not very informative.
• (I know is that cache restoring use a different algorithm in Windows compared to Ubuntu and MacOs, but this doesn’t explain the significant slowdown.)

I will experiment with removing the cache altogether in Windows to see if this speeds up the workflow.

[anakin87]

We disabled caching in #9318.

Over time, we should evaluate if it's worth re-enabling it.