Force corepack version to fix CI builds

[deedeeh]

What does this change?

This PR is to fix corepack in CI which is causes failing builds https://github.com/guardian/google-admanager-api/actions/runs/13178898620/job/36784637827?pr=29

The fix is inspired by guardian/support-service-lambdas#2666 and has been implemented in https://github.com/guardian/ad-manager-line-items-jobs/pull/19/files and guardian/commercial#1774

How to test

The build in this PR passes.

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Latest commit: fb45421

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