[data] update searx.data - update_firefox_version.py (#4954)

Co-authored-by: searxng-bot <searxng-bot@users.noreply.github.com>

searx/data/useragents.json

@@ -5,7 +5,7 @@
     ],
     "ua": "Mozilla/5.0 ({os}; rv:{version}) Gecko/20100101 Firefox/{version}",
     "versions": [
-        "139.0",
-        "138.0"
+        "140.0",
+        "139.0"
     ]
 }