Use a default `User-Agent` when downloading images (`Mozilla/5.0`)

docutils_extended/directives/embedded_image_directive.py

@@ -49,7 +49,7 @@ def load_and_convert_image(
         tmp_dir = None
     if image_is_remote:
         image_url = image_filepath_or_url
-        response = requests.get(image_url)
+        response = requests.get(image_url, headers={"User-Agent": "Mozilla/5.0"})
         response.raise_for_status()
         image_content = response.content
         if not convert_to_base64 or image_will_be_converted: