[fix] reduce error logs related to X-Forwarded-For & X-Real-IP headers

To test start a `make run` instance and query multiple times for `ip` (the
answerer), you should see only once the error message(s):

    ERROR   searx.botdetection            : X-Forwarded-For header is not set!
    ERROR   searx.botdetection            : X-Real-IP header is not set!

[1] https://github.com/searxng/searxng-docker/discussions/174
[2] https://github.com/searxng/searxng-docker/pull/162#issuecomment-1692834457



Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>