This has only been needed because we were flagged by HTTP2 fingerprinting.
Now, since we use curl cffi, we can bypass the fingerpinting, so we can
use HTTP2 just fine without getting blocked.
These engines override the user agent manually using `gen_useragent`, although that's already done in the online preprocessor that runs before the actual `request(query, params)` method is called. Hence, this call is duplicated.
Related:
- https://github.com/searxng/searxng/pull/4990#discussion_r2195142838
