CI: Main workflow failing

```
  Switch invariant: ["ocaml-base-compiler" {= "5.0.0~alpha0"}]
  [ERROR] Could not determine which packages to install for this switch:
    * Missing dependency:
      - ocaml-base-compiler > 5.6.1~
      no matching version
  
```

https://github.com/janestreet/base/actions/runs/25587914729/job/75120052617