Fixes #1910

Changes Proposed in this Pull Request

• Added job_category to the job RSS feed XML output in job_feed_item(), consistent with how job_type is already included.
• Job categories are comma-separated when multiple categories are assigned to a listing.

Testing Instructions

1. Ensure at least one job listing has a category assigned.
2. Visit the job RSS feed URL (e.g. /?feed=job_feed).
3. Confirm each feed item that has categories now includes a <job_listing:job_category> element, e.g.:

   <job_listing:job_category><![CDATA[Engineering, Design]]></job_listing:job_category>

4. Confirm feed items without a category omit the element entirely.
5. Confirm existing feed elements (location, job_type, company, salary) are unaffected.

Release Notes

• Job categories are now included in the job RSS feed XML output.

New or Updated Hooks and Templates

Deprecated Code

Screenshot / Video