`changelog-check` hangs indefinitely when there is an extra paren in the change entry PR list

We encountered an instance recently where the `changelog-check` script got stuck. It turned out that it was because of an extra open paren in a change entry, inside of the list of linked PRs:

Here is the run where it stalled: https://github.com/MetaMask/core/actions/runs/20099204043/job/57666868281?pr=7430

We should ensure the `changelog-check` action prints an error in this case rather than stalling.