chore: Ignore elixir dependency in renovate

It's a bit complicated to support the `-otp` postfix right now, so to
fix this right now, we'll just disable automatic updates for elixir.

renovate.json

@@ -10,6 +10,11 @@
       "groupName": "asdf tool versions",
       "description": "Keep in mind that Renovate currently does not support updating PostgreSQL via asdf.",
       "matchFileNames": [".tool-versions"]
+    },
+    {
+      "matchFileNames": [".tool-versions"],
+      "matchPackageNames": ["elixir"],
+      "enabled": false
     }
   ]
 }