Add missing 2.12 upgrade to nav menu (#20657)

Signed-off-by: Eric Fletcher <fletch3555@users.noreply.github.com>

mkdocs.yml

@@ -128,6 +128,7 @@ nav:
     - operator-manual/server-commands/additional-configuration-method.md
   - Upgrading:
     - operator-manual/upgrading/overview.md
+    - operator-manual/upgrading/2.11-2.12.md
     - operator-manual/upgrading/2.10-2.11.md
     - operator-manual/upgrading/2.9-2.10.md
     - operator-manual/upgrading/2.8-2.9.md