Update geolocation-hello-world.mdx (#20350)

Author: fauen

src/content/docs/workers/examples/geolocation-hello-world.mdx

@@ -133,7 +133,7 @@ async def on_fetch(request):
       </body>
     """
 
-    headers = Headers.new({"content-type": "text/htmlcharset=UTF-8"}.items())
+    headers = Headers.new({"content-type": "text/html;charset=UTF-8"}.items())
     return Response.new(html, headers=headers)
 ```