ci: adds a reusable workflow for linking issues

[yosefmaru]

Closes #23

[dougollerenshaw]

This is great! One question: we get the following warning in the actions log:

Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: actions/github-script@v7. Actions will be forced to run with Node.js 24 by default starting June 2nd, 2026. Node.js 20 will be removed from the runner on September 16th, 2026. Please check if updated versions of these actions are available that support Node.js 24. To opt into Node.js 24 now, set the FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true environment variable on the runner or in your workflow file. Once Node.js 24 becomes the default, you can temporarily opt out by setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

That's true for the existing workflows also. Looks like this will stop working after 9/16/26. Can you address that in this workflow? I'll also need to address it in other workflows, but maybe that's an excuse to put in another PR to use this reusable workflow instead of the copied version that's in many repos already.