Fix cache_prune::prune_unzipped test to match updated error message format (#12330)
## Summary
Fixes the failing `cache_prune::prune_unzipped` test that was causing CI
failures in my other PR (#12328) and others like PR #12327.
The error message format changed to show a specific version constraint
(`iniconfig<=2.0.0`) rather than the generic 'all versions' message.
This PR updates the test to expect the new, more specific error message.
## Test Plan
Ran `cargo test -p uv cache_prune::prune_unzipped` to verify the test
now passes.