Upgrade Forgejo to v1.21.6

Security update! https://forgejo.org/2024-02-release-v1-21-6-0/

Love how simple this is. I also followed the upgrade guide:
https://forgejo.org/docs/v1.21/admin/upgrade/

I did the dump (just a single command since we're on SQLite), and also
ran the `doctor`, and I broke the upgrade guidance a bit because it
returned some warnings that seemed pretty plainly non-blocking, e.g.
"orphaned OAuth2 applications belonging to no users" and stuff like
that.

setup-forgejo.yml

@@ -7,10 +7,12 @@
   tasks:
     - name: Download Forgejo binary to /usr/local/bin (and verify its checksum)
       get_url:
-        url: https://codeberg.org/forgejo/forgejo/releases/download/v1.21.3-0/forgejo-1.21.3-0-linux-amd64
+        url: https://codeberg.org/forgejo/forgejo/releases/download/v1.21.6-0/forgejo-1.21.6-0-linux-amd64
         dest: /usr/local/bin/forgejo
-        checksum: "sha256:8c8f34e889f968b4f9357701ceee7daab5b47ea605793325da8e3e740457b45a"
+        checksum: "sha256:e86f446236a287b9ba2c65f8ff7b0a9ea4f451a5ffc3134f416f751e1eecf97c"
         mode: "755"
+      notify:
+        - Restart Forgejo
 
     - name: Update apt cache
       apt: