Fix variable case in code snippet in docs (#9311)

- Description: Fix a minor variable naming inconsistency in a code
snippet in the docs
  - Issue: N/A
  - Dependencies: none
  - Tag maintainer: N/A
  - Twitter handle: N/A

docs/extras/use_cases/agents/wikibase_agent.ipynb

@@ -123,7 +123,7 @@
     "wikidata_user_agent_header = (\n",
     "    None\n",
     "    if not config.has_section(\"WIKIDATA\")\n",
-    "    else config[\"WIKIDATA\"][\"WIKIDAtA_USER_AGENT_HEADER\"]\n",
+    "    else config[\"WIKIDATA\"][\"WIKIDATA_USER_AGENT_HEADER\"]\n",
     ")"
    ]
   },