generate_pages.py: Search for only the "docs" jobs

By default, queries to gitlab are limited to 20 results each, ever since our pipelines became quite beefy, we've exceeded this 20 result limit and as a result, we have not published the docs from master since mid december.

Filtering the query and searching for only the "docs" job fixes this nicely (a less nice alternative would have been to use all=True in the list() method kwargs).