ci: use shared github action for contract tests

[cwaldren-ld]

• [x] Test with no Github token provided (succeeded at downloading the contract test binary)
• [x] Test with wrong token provided (gets a 404 error, token not redacted)
• [x] Test with correct token provided (works, token is redacted

In all cases, ensure real token isn't leaked anywhere in logs.

TODO:

• [x] Update the references to the gh-actions/contract-tests to an actual release number once the action is merged.

[shortcut-integration[bot]]

This pull request has been linked to Shortcut Story #231796: Refactor contract test workflow to use shared github action.