ci: Fix issue response script

[maxdeviant]

This PR fixes the issue response script.

There were a number of things preventing it from working:

• The directory name used in the GitHub Action did not match the one on disk.
  • The script has been moved accordingly
• ts-node does not support ESM.
  • ts-node seems unmaintained, so I changed the script to be plain JS that is type-checked with TypeScript.
• The data being sent to the Slack API was invalid:
  • Each section block can only have a maximum of 3000 characters in the text field, so we need to break up the issue list across multiple sections.
  • We needed to escape &, <, and > characters in the issue titles.

Release Notes:

• N/A