Fix fosstodon link (#493)

Author: jarrodmillman

doc/config.yaml

@@ -42,7 +42,7 @@ params:
         icon: github
       - link: https://www.youtube.com/c/ScientificPython-org
         icon: youtube
-      - link: https://fosstodon.org/scientific_python
+      - link: https://fosstodon.org/@scientific_python
         icon: mastodon
       - link: https://discuss.scientific-python.org
         icon: discourse