Join URLs with urljoin again

The base URL needs a trailing "/", so the part after the first "/" won't
be ignored.

PFERD/crawl/ilias/ilias_web_crawler.py

@@ -209,7 +209,7 @@ async def _run(self) -> None:
     async def _crawl_course(self, course_id: int) -> None:
         # Start crawling at the given course
         root_url = url_set_query_param(
-            self._base_url + "/goto.php",
+            urljoin(self._base_url + "/", "goto.php"),
             "target", f"crs_{course_id}",
         )