Fix get-demos CI: remove module.exports incompatible with Node 24 - #386

The get-demos job fails with ReferenceError: module is not defined because GitHub Actions runners now default to Node 24, where module is not available in the eval() context used by actions/github-script for inline scripts.

Changes

• .github/workflows/build-concurrently.yml: Removed the module.exports = ({core}) => { ... } wrapper from the inline github-script script. Inline scripts run as the body of an async function with core already in scope — module.exports is only valid for external script files, not inline usage.

// Before (broken on Node 24)
module.exports = ({core}) => {
  // ...
  return projectPaths;
}

// After
try {
  // ...
  return projectPaths;
} catch (error) {
  core.setFailed(error.message);
}