CI: ESLint upgrade breaks linting on Node.js 16.x

[buffalojoec]

Problem

Our JS test jobs for pull requests are using Node.js 20.5, but the workflows on master use 16.x.

This difference in Node.js versions breaks linting after the latest ESLint upgrade (#7257, #7258).

Proposed Solution

If we want PRs to test JS against Node.js 20.5 but keep master on 16.x, then we revert #7257 and #7258, since the newer ESLint uses structuredClone(), which is only available > Node,js 17.x.

Otherwise, we can increment the minimum supported Node version, but I don't think this makes sense to do for just linting. The libraries are still compatible with 16.x.